Clap Your Hands If You Believe

""He replied, 'If you have faith as small as a mustard seed, you can say to this mulberry tree, "Be uprooted and planted in the sea," and it will obey you.'""

- Jesus addressing his disciples, The Bible: Luke 17:5-6

An old trope, wherein enough belief in something will actually cause things to happen, also known as "magical thinking". This isn't a Magic Feather where "confidence" merely allows one to use their own abilities to the fullest; this actually physically changes the universe. In particular, a somewhat post-modern take on divine pantheons posits that gods are the product of (or severely dependent upon) their believers. Take away their believers, and a god "fades away."

This creates a vicious cycle for non-believers, as magical events are "disproved" in their presence because they don't believe in the first place, thus cementing their disbelief. Particular savvy characters may take advantage of this by getting others to yell "I'm Not Afraid of You!"

A variant of this trope crosses it with I Am Spartacus, with the hero asking the people watching the battle to lend their belief/hope/faith in order to help. A further variant, common in works aimed at children (and their parodies) involves one character turning to the audience and asking them to clap their hands/stomp their feet/whatever to accomplish whatever needs to be accomplished at the time.

This is frequently applied to how religious symbols effect vampires, making the faith repeal vampires instead of a symbol, as it avoids making a single faith "correct" in the context of the work but keeps the classic weakness.

The lead quote is from The Bible, making this Older Than Feudalism.

Not to be confused with Your Mind Makes It Real, which has more to do with characters getting physically hurt with The Power Of Imagination (though the two tropes do sometimes intertwine). For those who don't even need to clap, see Reality Warper. See also Puff of Logic, Psychoactive Powers, All Myths Are True, and The Treachery of Images. Has nothing to do with Clasp Your Hands If You Deceive.

Anime and Manga

 * Axis Powers Hetalia: Mystical ancient Shinto creatures and ghosts are disappearing and leaving Japan because not just the people of Japan but also Japan himself don't believe in them anymore. There's always England...
 * A popular Fanon theory has it that nations are manifestations of their respective countries' people, culture and national identity, not any political entities. They die when their culture fades away and no one identifies with them anymore.
 * In "The Land of the Will, Cephiro" in Magic Knight Rayearth, the "heart that believes" shapes the world around them.
 * The Mermaid Melody Pichi Pichi Pitch manga has the Purple Harp, which loses its strings when Lucia fears that she'll fail, and regains them when Hanon and Rina tell her to believe in herself.
 * The most recent chapter of Berserk:.
 * It doesn't stop there. Answering the wider question as to why the world of Berserk is so full of crapsuck,
 * The part where the trope crosses over with I Am Spartacus is the principle behind Goku's Genki-dama/Spirit Bomb in Dragon Ball: he draws energy from the Earth, including its people, to power it up. Addressed straight in
 * In the manga, Hyde and Closer, Shunpei and his animated magical chainsaw-wielding bear toy must fight off magicians out to kill him, all while learning magic in order to defend himself. Hyde explains that the source of all magical power is belief; the point of the strange rituals is to convince the spellcaster of the spell's reality.
 * In Kanon,
 * In Welcome to The NHK, a large number of the episodes are spent with the protagonist Tatsuhiro Sato having hallucinations of characters, scenarios, and people are members of an organization out to ruin his life. Near the end of the series, he asks one of the other cast members to see one of these creatures, where it is revealed to her.
 * In the Nasuverse, the Gods of old were willed into existence because people believed they exist. This also explains their downfall, as the number of believers declined... or because their believers think they all died in some massive slugfest (like Ragnarök). Other examples from Nasu include the summoned spirits of dead heroes, who become stronger if their legend is better known, and a weapon designed by the Catholic church for defeating a reincarnating vampire by shoving their belief that reincarnation doesn't exist forcibly down his throat. Or through his liver. Whatever works.
 * Spiral power in Tengen Toppa Gurren Lagann is given several different Techno Babble explanations, but the effective result is that if you truly believe you can win, you will win. (Possibly by virtue of a Humongous Mecha the size of a galaxy forming itself out of pure willpower.) Conversely, pilots afflicted with sudden pangs of doubt are apt to find their robots powering down, which is ruthlessly exploited by the Anti-Spirals, using tactics designed to induce fear and despair to try and shake that confidence.
 * It's also established that, due to Spiral Power, a Gunman's controls are set to how the pilot thinks it should be controlled. It's possible for someone with no prior training to get into a Gunman, move some joysticks, and get it working solely because that's what they want it to do.
 * A Certain Magical Index: 's incredible Reality Warper powers are limited by what he thinks his limits are; if he loses confidence in his power and stops believing in its effectiveness, reality obliges.
 * All espers derive their powers from having radically different internal realities from the standard. The process involves little kids, experimental drugs and brainwashing. Lots of parents seem to have no problems volunteering their kids for the process. Since the process is repeatable, it's Scientific, as opposed to the methods of the magicians... wait a minute.
 * In The Slayers, Shinzoku are dependent on the prayers of the mortal races, to the point where their counterparts, Mazoku, tactically destroyed temples to reduce the power of Shinzoku. Mazoku have their own form, feeding off of any negative emotions the mortal races have.
 * In the novels, Lina was once confronted by Dynast Graushera's General, a very powerful Mazoku. Realizing she couldn't fight or escape, Lina decided to try mocking said Mazoku's name. The reasoning was that because Mazoku were masses of astral energy held together by their own self image, anything that undermined their self confidence would make them weaker. The strategy works.
 * Full Metal Panic!: the Lambda Driver reacts to the user's mental state. The first time Sousuke uses it, Kaname instructs him that he must believe in it for it to work.
 * In Umineko no Naku Koro ni, the point of Battler's game with the witch Beatrice is that, should he accept her existence and the existence of magic, magic will exist in retrospect as the cause of the murders that drive the whole mystery. Since he refuses to accept her existence, though, Beatrice must prove her existence with new unsolvable murders.
 * This is also poor dilemma in Higurashi no Naku Koro ni, as lack of faith by the residents is the cause of the character's weakened powers.
 * A not-so-nice version is a major plot point in Paranoia Agent., and unpleasant, freaky, and completely incomprehensible things ensued.
 * In Mahou Sensei Negima, apparently you only have a soul if you believe you have one.
 * In Fate/kaleid liner Prisma Illya, the main character Illya, can fly because she was a fan of Magical Girls before becoming one and believes that all Magical Girls have to be able to fly. Miyu on the other hand, can't fly because she is smart and can't ignore the laws of physics.
 * Pokémon 3 crossed this trope with Reality Warping, resulting in the Unown being driven crazy by their own creation, and then being stopped by Entei when Molly Hale began believing in him.

Comic Books
"You've read too much fiction, Arnicus. Gods are not dependent on their worshipers; worshipers are dependent on their gods. And the New Gods? We're as old as time, constantly remade, constantly reborn with each turning of the wheel. No worshipers? Fool!!! Look about you! Each time a mortal turns on a computer, puts a piece of bread in the toaster, opens a door, strikes a match, or wonders at the stars... ...he worships at the altar of the New Gods."
 * The living myths in Fables are made stronger by those who believe in them. This is used to explain why some lesser-known fables are killed, but Snow White can take a rifle shot to the head and survive, albeit with long-term consequences.
 * This is turned into a plot point later, when Jack Horner (of "Jack and the Beanstalk," "Jack The Giant Killer," and several other stories) decides to increase his personal power by releasing a series of Hollywood blockbusters about himself.
 * Subverted by.
 * The DC Comics character Dr. Thirteen was a skeptic who disproved hauntings. Since he was established as existing in The DCU, and eventually encountered The Phantom Stranger, the fact he was always right in his own stories seemed strange and turned him into a Flat Earth Atheist, until Neil Gaiman's Books of Magic explained that his complete dismissal of magic meant he lived in a personal world where there was none.
 * Excalibur member Meggan was an empathic adaptive shapeshifter—she looked like what people expected her to look like, and consequently spent a good part of her childhood turning into a monster. Eventually, she managed to develop a strong enough sense of identity that other people's expectations no longer affected her shapeshifting.
 * In one of those cosmic ironies, the current powerset of Captain Britain, Meggan's husband, depends on his own confidence, much like Gladiator below - the stronger his confidence, the stronger he becomes.
 * Another example from the Marvel Universe is the Shi'ar Imperial Guard commander Gladiator: His strength is based on his own belief in his power. Shake his confidence and he can be beaten easily, rev it up and he crushes stars with his fists.
 * His son Kid Gladiator has the same basic powers and an even bigger ego, being a teenager and all. Nothing, not even temporarily being turned into a Brood, has managed to shake him up.
 * According to Marvel Adventures (and possibly main 616 canon), Dr. Strange's magic works the same way. He deliberately cultivates a Large Ham persona to boost his own confidence.
 * Yet another example from the Marvel Universe are the Cardinals, who serve as the elite shock troops/assassins for the Universal Church of Truth. The Church collects the Prayer Power of it's trillion-plus faithful worshipers, then converts that prayer power into energy and stores it in belief batteries. The Cardinals can tap into that immense power reserve, giving them the power to do anything if they believe they can. Hence the Cardinals can shoot energy beams, create force fields, and etc. because some convert on the other side of the galaxy believes they can do that.
 * It doesn't even have somebody else, it could be the Cardinal himself who believes.
 * In the August 1966 issue of The Flash, Barry Allen starts to fade away from existence once a villain unleashes a ray that causes everyone to not believe he exists. Everyone except a little orphan girl he had helped before forgets that he really exists until he and the orphan girl start a massive letter writing campaign to force people to remember The Flash.
 * This issue is somewhat prescient considering that the DCU contains an actual comic book limbo where characters (often those who haven't appeared in books for quite some time in the real world) go to when people start to forget their stories.
 * This is central to one of Warren Ellis' stories for Hellblazer. An occult writer "acquires" a magical item called The Crib, and sets about killing people with it. The thing is, there's no such artifact, and it only works because both he and his victims believed in it. John Constantine, being more knowledgeable about the truth of the occult world, knows there's no such item, so it has no effect on him, and he's able to reveal what the person actually had—an old cereal box with a dead mouse in it. It's discussed in earlier stories that magic in general works on this principle, but this is the first one where it really takes center stage and we see just how far it goes.
 * Gods and other supernatural beings in Neil Gaiman's The Sandman live off of this trope which shows up in his other writings as well.
 * When they turn up in a Grant Morrison issue of Justice League of America, the heroes are sent into a boy's nightmare world, where a telepathic conqueror has created a world where it has already won and there are no heroes to stop it. As the boy's belief wanes, so do their powers.
 * Subverted by Walt Simonson in Orion # 24:


 * Used in Marvel Comics in Thor # 301, where it was revealed that, while the gods themselves could exist long after they had no more worshipers, those who STILL have some had greater amounts of power. Also, a god is stronger in his home plane than gods from another.
 * In Thor Meets Captain America by David Brin, this trope is used by the hero. His actual words are "I don't believe in you".
 * When the X-Men faced off with Dracula, Kitty Pryde tries using a crucifix against Dracula and achieves nothing. Dracula then grabs her throat, and burns his hand on her Star of David necklace. No points for guessing Kitty's religion, folks!
 * Wolverine is unable to repel Dracula with a cross, but when devout Nightcrawler takes up the symbol, Drac is driven back.
 * In Crimson, it's apparently the vampire's religious background that counts, as one man learns when the vampire he's trying to ward off takes his cross away and beats him with it, remarking "My name is Steinman, schmuck! Why would this work on me?"

Film
"Booboo: This is the part where he goes Tinkerbell on us."
 * In Yogi Bear and the Magical Flight of the Spruce Goose Yogi gets his friends out of the cargo hold of the eponymous airplane by having them believe a set of doors into existence.

"Phil Moskowitz: No bullets? Ah, but if all of you in the audience who believe in fairies will clap your hands, then my gun will be magically filled with bullets."
 * Inverted in The Flight of Dragons where the protagonist Peter defeats the evil wizard Omadon by 'denying' that he exists, and since magic relies on human belief to exist Omadon crumbles away to nothing.
 * In Freddy vs. Jason, Freddy Krueger's weakness is that he only has power so long as people believe in him, so he has to bring Jason back to remind them. This hearkens back to the original ending for A Nightmare on Elm Street, where he's defeated by Nancy refusing to believe in and fear him any longer, robbing him of his powers - in the theatrical release, this only appears to work.
 * In Candyman the eponymous character was actually created by the people's belief. The sequels, though, are a different story...
 * Interestingly enough, after
 * In the horror movie The Skeleton Key, it is claimed the African witchcraft of Hoodoo can only be used on those who believe it. The plot plays with the notion that this means it's only psychology and suggestion (if you believe you were witchcrafted, you'll just act as if you did). However, the scientific approach is eventually abandoned. Once the antagonists finally manage to get the protagonist convinced that it's real, they can perform supernatural witchcraft on her. They then proclaim it's getting tougher for them to use witchcraft on new victims, as it's getting harder and harder to convince modern people that it's real.
 * Parodied in Woody Allen's Whats Up Tiger Lily.

"Peter Vincent: [brandishing a crucifix] Back, spawn of Satan! Jerry Dandrige: [chuckles] Oh, really? [grabs the cross, crushes it, and throws it aside] You have to have faith for this to work on me."
 * A woman in Feast II: Sloppy Seconds tries to believe her way out of terrible situation after terrible situation.
 * Andrei Tarkovsky is fond of this one: STALKER (not STALKER), Solaris (not Solaris).
 * In The Matrix the red pill humans are able to perform seemingly superhuman feats by believing that they can do it, since they're in a virtual reality. As Spoon Boy elaborates: "There is no spoon." There are limits to even their abilities, though, which is what makes Neo, whose belief can transcend those limits as well, so important (at least, that's how it seems at first).
 * Used at the end of the first Power Rangers movie to repair their decimated hidden base and restore Zordon to full health.
 * Care Bears Movie II: A New Generation, in which the audience is encouraged to say "I care!" to save a dying little girl, which not only succeeds, but acts as Love Redeems for the Big Bad.
 * In John Carpenter's In the Mouth of Madness, which pays homage to both Stephen King and H.P. Lovecraft, we see just how terrible the consequences of this trope can really be.
 * In Wes Cravens New Nightmare
 * Parodied in the first film of The Mummy Trilogy - Imhotep's soon-to-be Renfield tries to fend him off with a cross and a murmured Lord's Prayer, which is utterly useless. He then runs through a keychain of similar holy symbols and their matching incantations, none of which have any effect until he yanks out a Star of David and starts babbling in Hebrew - which the undead priest recognizes as "the language of the slaves," which makes Beni useful to him as a translator. Discussion of the actual use of Hebrew slaves in ancient Egypt and the language they spoke at time is reserved for other places...
 * Parodied again in Dracula 2000. One of Team Good Guy brandishes a crucifix at one of the vamps, who remarks "Sorry, sport. I'm an Atheist." The good guy wittily remarks "God loves you anyway." before stabbing the vamp in the eye with the knife hidden inside the crucifix.
 * R. L. Stine's The Haunting Hour: Don't Think About It Dont Think About It presents a rather twisted version of this by having The Evil Thing only exist as long as at least one person thinks about it, but making it almost impossible not to do so (if you'd read about a monster that vicious in a book, you'd think about it too.)
 * In Star Wars: The Empire Strikes Back, Yoda blames Luke's failure to levitate his X-wing out of the swamp on his not believing that such a feat is possible.
 * In Erik the Viking, Harald the Missionary who accompanies the Vikings on their quest staunchly refuses to believe in Ragnarok and any of the Viking myths. Eventually, the Vikings make their way to Valhalla, where they triumphantly demand that the missionary accept that they were right all along - only to discover that because he doesn't believe in it, he can't actually see it, and causing a certain amount of frustration. This actually saves them in the end, as because Harald doesn't believe in the Aesir they have no power over him. He can walk through the walls of Valhalla, make it back to the ship, and use the MacGuffin to bring them all back home while the other Vikings are trapped.
 * In The Fearless Vampire Killers (or Pardon Me But Your Teeth are in My Neck), a cross fails to work on a Jewish vampire.
 * In the mock documentary at the end of the film, an expert on vampires notes that the effectiveness of the religious symbol depends not on the human wielding it, but the vampire itself. Crosses work on Christians, Stars of Davids work on Jews - but the expert warns that using a Star of David on an Arab vampire will only make it angry.
 * Fright Night.


 * The Fright Night (2011 film) remake did this too, except with Charley holding the cross instead of Peter. The vampire simply feigns weakness before grabbing the cross with one hand and pinning Charley to a car with the other. The cross catches fire as he touches it, but he blows it out without even flinching.
 * In the Jim Carrey vehicle Once Bitten, The Countess shrugs off the religious symbol ("Put down the cross, Robin. It only works in movies. Besides, I'm an atheist.") Then Mark shows up with a torch, and the Countess recoils, declaring, "Fire, on the other hand..."

Literature
"There's an urban folk-myth that every time a human says he doesn't believe in dragons, a dragon dies. This is unlikely, because if it were true, we'd spend half our lives shovelling thirty-foot corpses out of the highways with dumper trucks and the smell would be intolerable. There's an old saying among dragons that every time a human says he doesn't believe in dragons, a human dies, and serve the cheeky bugger right."
 * The Trope Namer comes from a famous scene from Peter Pan. In this verse, a fairy is mortally wounded any time a child says "I d*n't believe in fairies;" in the scene in question, Peter uses the effect in reverse to save the fairy Tinker Bell's life by calling on children everywhere to indicate that they do believe in fairies. (In the original stage version - which predates the novel and the various film and television adaptations - this was an audience participation bit...and, in case you're wondering, if the audience is a bunch of heartless bastards who won't clap the orchestra is instructed to begin the applause.)
 * Tom Holt spoofed this scene in Open Sesame; a fairy provides medical care by shouting "I do believe in humans!"
 * And again in Paint Your Dragon:

"That wasn't enough. You didn't clap hard enough. Tinkerbell's dead."
 * The Christopher Durang play Dentity Crisis references this scene and the ensuing subversion from the fed-up actress playing Peter Pan who decides to sabotage it in the worst way possible:

""What happens to people after they die is what they believe will happen. The people who go to hell are the ones who believe, deep down in their hearts, that they deserve it. However, if you've never heard of hell before, it's impossible to believe in it. That is why it is important to kill missionaries on sight.""
 * Crowning Moment of Heartwarming: On the first night the original play was performed, they didn't know what would happen. When Nina Boucicault as Peter called out "Clap your hands!" there was an immediate deluge of applause, some people even stood up. Boucicault was so overwhelmed she began to cry.
 * C. S. Friedman's Coldfire Trilogy features a substance called fae which responds to brain activity and can do anything. This is used as a justification for Functional Magic as well as Clap Your Hands If You Believe. A clever fae hack involved spreading a made-up religion in order to change the natural laws.
 * Fae is also nasty. It doesn't just make for "proactive" magic; things based entirely on natural laws DON'T work if their user has any fear they might malfunction. Hear a bump in the night, and the fae will play on your instinctive fear to fill in what might have made it... The vicious cycle goes straight down into scenarios that approach Cosmic Horror Story. Furthermore, even the slightest belief that a device such as a gun could backfire will make it backfire; the fae makes Murphy's Law even worse. This is why the setting has been stuck in Medieval Stasis for 1000 years at the series' start.
 * The title character of The Dresden Files has little or no faith in the Almighty, so crosses don't ward off vampires for him. However, he has loads of faith in magic, and so his silver pentacle charm (a symbol of magic) works very well in putting aforementioned fang-faces in their place.
 * His sometime ally Michael is a devout believer however, so the Cross works just fine, as does his named sword and since Michael is a Knight of the Cross his bare hands work equally well. (He's not called the Fist of God as a pet name, folks!) When a Red Court vampire (who are not as vulnerable to faith as the Black Court) mocks the idea that Michael's faith in the cross will defend him, she lightly places a finger on one of the crosses stitched into his cloak, and she instantly bursts into white flames.
 * Faith in God himself is not necessary for a Knight of the Cross. Of the three knights presented so far, only Michael is particularly religious. Shiro was confused when he was being converted (though he tries his best to be a good Baptist regardless) and Sanya is Agnostic. It's their belief in defending the common man against evil that gives the knights their powers. It just happens that in Michael's case, this belief manifest itself as Christian Faith.
 * Dresden, being the First-Person Smartass he is, goes on to mock this trope during the climax of the fourth book, Summer Knight, by charging into a Fae battle screaming "I don't believe in faeries!!" Doesn't help him kill any Fae any better, but certainly is good for the adrenaline.
 * However, this apparently does work when fairies gain confidence in their own abilities: the more Toot-toot accomplishes on Harry's behalf, the bigger he gets. In the first book he is only six inches tall; by the 12th book, he is more than 15 inches tall and described as "ridiculously tall." Or alternatively, it was the result of him becoming the leader of the "Za Lords" and gaining followers.
 * Magic in the Dresdenverse requires belief in whatever the caster is doing. A caster cannot produce a spell if they do not, deep down, believe in the reasons behind why they are casting the spell. This is actually a small but critical plot point in Turn Coat, where LaFortier's murder involved no magic being slung. It is eventually revealed that the killer
 * In the Novella Backup, Thomas and Lara Raith are members of a secret society which fights against creatures who take their power from other people believing in them. The only way to assure victory is to limit as much as possible the number of people who know about the enemy (optimally: zero), making for some of the most severe "need-to-know" requirements ever faced by any army. (Being vampires, the Raiths aren't in it for the good of humanity, but rather to protect their food supply.)
 * The Faction Paradox beings known as the Celestis are actually ascended beings that are tethered in reality by nothing more than the power of others' belief in them; therefore, they appear as gods or demons wherever they choose to manifest.
 * In Stephen King's IT, the eponymous shapeshifting monster takes the form of a werewolf, making it vulnerable to silver simply because the child heroes of the book firmly believe that werewolves have to be vulnerable to silver. Also, believing that his inhaler was full of poison allowed a protagonist to harm It with the contents.
 * Established in King's writing much earlier in his short story The Boogeyman, which is in many ways a precursor to IT.
 * A cross does not work on a vampire in Salems Lot because its owner has lost his faith. When that character faces vampires again in a later King book, he has recovered his faith and is able to (briefly) drive them off, even after he puts the cross aside - it's only a symbol, after all.
 * The page quote isn't the only example from The Bible: e.g., in the Gospels, Simon Peter walks on water until he starts to doubt.
 * Stephen Colbert (apparently sincerely) believes this to be an instance of comic relief in the Bible, saying Jesus wouldn't be truly human if he could witness that without laughing.
 * In I Am Legend, vampires fear the holy symbol of what they believed in before they became vampires. The Protagonist's archenemy is terrified by the Star of David.
 * In Christopher Stasheff's Warlock of Gramaraye series, the planet Gramarye has a native fungus known as "witch-moss" which can assume animated forms based on the thoughts of those with latent Psychic Powers. Since five centuries of inbreeding has spread those genes to half the population, a lot of fairy tale creatures have since become real; if they become too real, and there's some of both genders, they can even mate and have fixed-form offspring, essentially creating a whole new species. The Wee Folk were born this way and can somehow interbreed with humans, producing fully fertile offspring.
 * Good Omens not only explicitly uses this concept as the core of its magic system, but actually introduces a system which measures the intensity of belief in one of its footnotes.
 * This appears to be the driving force behind mythological beings in the Logical Magician series of books by Robert Weinberg. In the second book, an Amazon (naturally, exceedingly beautiful) serving as a weapons instructor is explicitly confronted by the main character with theories regarding the rather hideous appearance of historical amazon women; he's rebuffed with "Maybe the real ones were. We aren't." Applies to myths both old and new; one of the most feared mythological beings around is 'The Man'. Also given an interesting inversion;
 * I'd mention Michael Crichton's The Sphere but that would spoil that plot.
 * Oops.
 * A variant occurs in the Harold Shea stories by L Sprague De Camp and Fletcher Pratt, in which it's possible to travel to another world by believing in the logical principles that govern that world. The place you're going was real to begin with (even though they're all based on mythology or literature), but believing the right things makes it accessible to your senses.
 * Lord Dunsany uses this. To say where would spoil an excellent short story.
 * Goes horribly, horribly wrong in regard to the "Stuff" in The Gone-Away World by Nick Harkaway. It becomes not what you believe, but what you're thinking of—and if you're thinking of ten things at once, it'll become a splice of all 10 things. This gets even worse if you get covered in Stuff.
 * The gods in the Discworld series work like this. The climax of Monstrous Regiment involved In Hogfather, when the Big Bad was magically preventing people from believing in the local equivalent of Santa Claus, the extra, unused belief-energy made any imaginary creature that was even slightly plausible (like a creature that eats odd socks, and a bird that eats pencil stubs) come into existence. Small Gods describes in detail how gods come into existence and become powerful.
 * "Belief" is stated as a very powerful force on the Discworld - if enough people believe something to be true, it will become true, however there are limits. The rules have never been fully stated, but it appears there needs to be a "space" that makes it somewhat reasonable such a thing could be true (hence the non-existence of the Give-The-Dean-A-Big-Bag-Of-Money goblin). In Pyramids the mess of multiple combined mythologies that made up the religion of Djelibeybi, much of which was self-contradictory, and a lot of which could be contradicted by simple observation, only became true when the kingdom was pushed into an alternate reality with an even lower reality threshold than the Disc.
 * An evil witch set herself up as secret ruler of the Magic Kingdom of Genua in Witches Abroad by manipulating the lives of people and reality itself by bending fairy tales around herself.
 * In Carpe Jugulum, one family of vampires have developed the ability to resist religious symbols (as well as most things that vampires are traditionally vulnerable to) through extensive psychological conditioning.
 * later expanded into the Black Ribbon Society, which provided a better integration with a multicultural modern city
 * The New Discworld Companion has as Watch standard gear, "One holy symbol of recruit's choice, vampires, for the discouragement of. One Critique of Pure Reason, vampires, for the discouragement of (Freethinker's option)." This was before a vampire joined the Watch...
 * What happens to people on the Discworld after they die is determined by what they believe. Not necessarily what they want, but what they believe. In Small Gods, there is a character who believes in Om, but after he dies he thinks about what he believes and it's implied that he has a slightly different outcome than other Om believers. He has a different outlook on life than other Om believers, and therefore, something different would happen to him.

"Narrator: The ancient prophets may have had faith strong enough to move mountains. But Uncle Otis was possessed of something far more remarkable, it seemed - a lack of faith which could unmove them."
 * Fred Saberhagen's Book of Swords series had this as a plot development. The gods, including such familiar names as the war god Mars and Vulcan the smith, are bored. To entertain themselves, they play a game with humanity: 12 highly powerful magic swords are created, and spread throughout the lands purely to incite wars amongst the various nations. The plan backfires when, thanks to the highly visible power of the various swords, mankind's belief in the gods wane and is replaced by belief in the swords. Consequently, the gods rapidly weaken and die.
 * In the interquel novel Ardneh's Sword, which was written years later and is widely regarded as Discontinuity by many fans, it is explained that the Gods . It seems likely that their apparent dependance on belief was psychosomatic at first, but became this trope over time.
 * In John C. Wright's Chronicles of Chaos, this is one technique of Functional Magic, where the character can make true what he wants to be true. Its weakness is that he really has to want it; if you do not actually feel the malice necessary, you can not curse someone, for instance.
 * Subverted in F. Paul Wilson's The Keep, in which a "vampire" pretends to be affected by a Christian cross, but not a Star of David in order to cause a Jewish professor to question his faith.
 * In The Haunting of Alaizabel Cray, there's an interesting case:
 * There is a short story in which a demon has the job of dragging humans to Hell, and can only be defeated by holy words. The specific religion doesn't matter so much as the strength of the person's belief. His first intended victim is a Christian who prays and forces him to let go. The second is an atheist, and her holy words are the laws of physics. Hilarity Ensues.
 * Anyone here know what the story is?
 * In the Eisenhorn novel Malleus, the title character is able to severely weaken a Chaos-corrupted stone by recording himself reciting one of the (many) Imperial declarations of faith and continually transmitting the recording into the stone.
 * In the third book Hereticus, after Eisenhorn is forced to in order to defeat, he then tries to weaken him by reciting The Benediction of Terra. However by that point Eisenhorn has been both physically and mentally drained and couldn't force his will enough for the prayer to actually have effect. On the other hand, a crazed Imperial priest who witnesses all of this manages to scare off  by mistaking him for a manifestation of the Emperor's power and running at him at full speed, chanting praises for the Emperor and holding a holy Imperial Aquilla, hurting  with the sheer force of his belief in the Emperor.
 * In Neil Gaiman's American Gods, gods and supernatural creatures are made real and powerful by worship and belief, and fade away and die when people stop believing in them.
 * In Monster Hunter International holy symbols have power over undead monsters by virtue of the belief placed in them. However, the biggest act of faith-based ass kicking comes from.
 * Deconstructed in Kingdom Keepers. Enough people believing in them is what causes several Disney characters to come to life...including the villains, who are putting the world in danger.
 * In Sergey Lukyanenko's Star Shadow, it is eventually revealed that the human jump drives work because the pilots believe them to work. This is also why humans are the only ones who retain their sanity when using it - because this should not be possible. The protagonist even recalls that the jumper was invented by a bunch of underfunded Russian researchers, and the scientific basis for the device was added as an afterthought and seems tacked-on. Also, every jumper works exactly the same, no matter the design or power. Kinda makes sense since astronauts have to believe they'll succeed in order not to die.
 * In explaining the history of money Dave Barry specifically uses the Tinker Bell scene as an analogy for how money works these days (i.e. no longer tied to gold or another precious metal). We all believe currency has value, so it does.
 * A rare inversion with a short story ("Obstinate Uncle Otis") about an obstinate Vermonter (and as such, the most obstinate man in the world) whose power of disbelief was legendary, to the point where he could almost convince others that their eyes were tricking them. And then he got struck by lightning, and got a dose of Your Mind Makes It Reality. The statue in the town square to the man he hated? Gone after he commented about how "No one would build a statue to a nincompoop like that!" The barn that was obstructing a nice view? Also gone when he commented how "No barn there, boy! Nothing but th' view - finest view in Vermont." His nephew realizes the danger this poses (e.g. his hatred of Franklin Roosevelt, his recent disbelief in stars, etc.). It comes back to bite the elderly man on the ass, though, as he got a bit of Easy Amnesia and believed himself to be a traveling salesman with a different name. "Humph - ain't no such person as Otis Morks."
 * And before Fridge Horror enters into it, the narrator was also named Otis Morks, yet didn't disappear - unlike his hapless, obstinate Uncle.


 * Skeeve from Myth Adventures is struggling to teach his apprentice Massha to light a candle via magic when he realizes she doesn't actually believe she's capable of such a thing. When he encourages her to visualize a magical trinket (a form of magic she does believe in) inducing the same effect, she succeeds in setting the candle alight.
 * The basis of all magic in the Shannara series.
 * In David Eddings's Elenium and Tamuli series, gods can be destroyed by killing all their worshipers. This is actually used as an offensive technique by.
 * Some gods in Steven Erikson's Malazan Book of the Fallen are formed from the belief of their adherents and die if they are forgotten. Others are independently existing beings whose divine powers are powered by worship.
 * An early example: In A. E. Van Vogt's Book of Pthah gods and goddesses are ordinary humans who have immortality and supernatural powers by the virtue of being worshiped by great numbers of the opposite sex.
 * In Christopher Moore's Coyote Blue, this will happen to Coyote, and did happen to his brother, if people stop believing in him and telling his stories. Coyote fears this so much that he allows so that people will still talk about him.
 * All Myths Are True in Douglas Adams' The Long Dark Tea Time of the Soul because of this effect. The old gods, like Odin, are languishing but a new is created, possibly from society as a whole, but also possibly from the eccentricities of Dirk Gently alone.
 * The Hitchhiker's Guide to the Galaxy has a theory on God's non-existence as a guide entry. Shortly, it goes like this: Since nothing can as useful as the Babelfish can be born through coincidence, this proves God's existence, but with knowledge, there isn't faith, and without faith, God is nothing. This seems to follow the same logic.
 * By the time Dracula was written, vampire lore included an aversion to a cross. This, in different series, can be either the product of the vampire's belief in the cross, or the product of the wielder's belief in the cross. Often, it also works with another strong symbol of belief - for example, a rabbi using a Star of David to hold a vampire at bay. See: Our Vampires Are Different.
 * Subverted in Blindsight; the vampires and crosses thing is not because of anything religious or mystical but because their brains go into seizure when exposed to straight vertical and horizontal objects in their visual field forming a 90 degree angle (not as dumb as it sounds: there are people who have similar types of problems due to head trauma). That sort of thing is not that common in nature, and it wasn't much of a problem until their food source went and invented architecture and drove them into extinction.
 * Subverted in Christopher Golden's Shadow Saga in that the effects of the cross on vampires is purely psychosomatic because

Live Action TV

 * Power Rangers Mystic Force: The key component to being able to use magic is, it seems, believing in magic. In the premiere, Nick is unable to use magic because he doesn't believe - even after he's seen others using it (and despite considerable effort 'trying' to believe). He gains the ability to cast spells only after announcing that he really does, after all, believe in magic. In the finale, the entire city's belief is used as a Combined Energy Attack.
 * An episode of Star Trek: The Original Series has the crew find a pulled-from-myth planet of Ancient Greece, presided over by Apollo, who laments that the rest of the gods perished, more or less, from a lack of followers.
 * The Star Trek Expanded Universe has "the Beings" in Peter David's Star Trek: New Frontier series, who gained power from worship and fear, and inverted when it turned out the most powerful among them was so because he gained power from peoples' belief in themselves.
 * Also in the Expanded Universe is the novel Gods Above, featuring more Beings like Apollo who not only thrive on worship, but on fear and doubt as well. The only way for the crew to defeat them is to be truly fearless.
 * An early Star Trek: The Next Generation episode had a Sufficiently Advanced Alien known as The Traveler strengthened by the entire Enterprise crew concentrating on making him better. (Granted, they were in an area of the universe where thoughts become reality, but it still fits the trope).
 * The Stargate SG-1 Big Bad of seasons 9 and 10, the Ori, are ascended beings who thrive on worship. And they also lose their powers when not worshiped, A fitting end.
 * The Big Bads of the previous eight seasons, the Goa'uld, are a more figurative example. Once a significant number of people stop believing that a particular Goa'uld is a god, it's usually a sign that said Goa'uld is about to lose out.
 * The finale of the Doctor Who new series third season came under some fire for relying on this, albeit with a Hand Wave involving a Phlebotinum assisted telepathic field that focused the belief, causing what fans call TinkerBell Jesus or Fairy Doctor.
 * In the fifth season finale It... sort of makes sense in context.
 * Earlier, in "The Curse of Fenric", a cross works only if the bearer has faith in it, and other objects of faith work equally well: a WWII Russian soldier fends off vampires with a soviet badge, and both the Doctor and Ace are able to hold them at bay with no physical object, through their faith in each other. The priest who doubts his faith however...
 * An episode of Supernatural focused on a spirit that was created (and maintained) by people's belief in it. Unfortunately, getting people to stop believing was not an option.
 * Leading Sam to wonder how many of the things they hunt only exist because people believe in them.
 * In the Buffy the Vampire Slayer episode "Out of Sight, Out of Mind," a girl is actually rendered invisible because no one ever noticed her (an effect heightened by the school she attends being built over a hellmouth).
 * Toyed with in Dead Like Me. The recently deceased will cross-over with the gateways to the next world taking a form that appeals to them. In the pilot, a little girl sees a huge spectral carnival; in a later episode, the soul of an old yet feisty man of indeterminate UK clearly Irish origin leaps from the precipice of a chalk cliff the Cliffs of Dover.
 * Nickelodeon's Kids Choice Awards 2008 has a character called the Rocktopus (a rock and roll octopus who wears shades) and during the end where Jack Black and Orlando Bloom are doing the final slime stunt - there's no slime coming out at first because the machine requires someone with 8 arms to operate it, and the Rocktopus happens to be the one that fits that - the only problem is that he needs encouragement from the audience - so the audience give him encouragement by shouting... "Slime! Slime! Slime! Slime! Slime! Slime!"
 * In one episode of Bottom, Richie and Eddie are saved from a Ferris Wheel by the hand of God. When they remember that they don't believe in God, the hand vanishes and they fall to their doom.
 * In the TV miniseries Merlin, Merlin finally defeats the evil Queen Mab by encouraging everyone to forget about her. This is the culmination of the fading belief in her and led to her vanishing. The novelizations went as far as noting that Merlin omitted her from his stories about the events and misattributed them to Mordred or Morgan le Fay.
 * One episode of Fraggle Rock introduced a one-off character named Skinfred, a small monster whose transformations were based upon this Trope. His physical appearance depended on what other people thought about him (it's impressive how upbeat his personality was given how very definitely Blessed with Suck he was). Red and Wembly like him, think he's very cute and friendly... and that he sports goofy pigtails. Ma Gorge does not like him, thinks he's creepy and scary for living in her flooded basement, and wonders if he's actually a giant, fanged, two-headed monster. Guess what happens next. (Skinfred: "Aw, I hate having to be a monster!")
 * A similar creature appeared in the Fraggle Rock comic book. The cast had to deal with a considerably less friendly monster who was also exactly as tough as an opponent believed it to be, resulting into hilarious scenes of our heroes making things worse and worse. "I don't care if you're fifty feet tall..." * Poof! Monster is now fifty feet tall*
 * Stephen Colbert fully believes in this trope, naming it Wikiality, wherein if enough people believe something to be fact, it is; and the best method for altering the public's belief in something? Change its Wikipedia page.
 * To demonstrate this, he single-handedly tripled the African Elephants' numbers via Wikipedia. Quite a feat.
 * Lettie Mae, Tara's mother, in True Blood gets rid of a "demon" that makes her an alcoholic via exorcism. It turns out to be a scam, but that doesn't faze Lettie Mae.
 * This also works on Tara as well, for a while, at least. Then she finds out it was all a scam and becomes her old "friendly" self. Then a maenad shows up and tells Tara it was her belief that called her to Bon Temps.
 * One episode of Wire in The Blood dealt with this trope. The murderer of the story was thought by some people to be using magic. Tony Hill, however, knew that it was all in the victims' heads and when the murderer was finally caught, she thought Tony was a powerful wizard because he'd been able to see through her "invisibility".
 * In Community episode "Epidemiology" it was brought up and then thoroughly subverted.
 * In the 1998 Merlin-1998 series, The Fair Folk and gods of Celtic Mythology don't necessarily require followers and prayers (though it helps), but they absolutely need to have people believe in them. If people stop believing in them and ascribing importance to them, they will simply cease to exist.
 * In Being Human (UK), vampires recoil from George's Star of David pendant. But George's affection for his best friend Mitchell (who is a vampire) makes Mitchell immune to its deleterious effects. Mitchell even keeps the necklace safe when George transforms.

Professional Wrestling

 * During one storyline in the early-to-mid-nineties Kama stole The Undertaker's urn of power. The Undertaker said that he now had to rely on his Creatures of the Night (his special nickname for his fans) to provide him with the power he needed to win the match.

Tabletop Games

 * In the Old World of Darkness:
 * In Mage: The Ascension, reality is the result of consensus belief; normal humans who haven't pierced the Masquerade can disrupt magic through disbelief. "That can't happen," they think, and their belief is strong enough to make it unhappen, make them forget it ever happened, and punish the mage for his attempt. Conversely, mages have carefully-constructed belief systems that allow them to impose their wills upon reality and reshape it as they see fit. For example, the Earth never used to orbit the Sun, steam power never used to be possible, until the Technocracy managed to make most of humanity believe in it.
 * In Hunter: The Reckoning the collective force of human belief makes supernatural phenomena simply invisible to most people.
 * Changeling: The Dreaming had this as a central element of the story; since humanity considers fairy tales to be, well, fairy tales, changelings consider themselves to be an endangered species, and the discouragement of freedom and the imagination (known as Banality) is actually toxic to them.
 * Vampire: The Masquerade, vampires aren't averted by crosses or other holy symbols unless the wielder's faith is particularly strong. In addition, a vampire character may purchase a number of supernatural flaws that are common to vampire lore: be it being repulsed by crosses, being unable to cross running water, being unable to enter a house uninvited... Depending on the DM and player's interpretation, those flaws are either factual problems caused by the character's particular bloodline (after all, someone must have given rise to those myths, and that someone probably sired other vampires) or this trope: the vampire fears garlic, because he's convinced vampires do.
 * The demons in Demon: The Fallen power their abilities through the harvesting of faith from humans. This can be done quickly, through "reaping" (kind or cruel as the demon wishes), or on a long-term basis by making a pact with a human.
 * In the New World of Darkness:
 * In Mage: The Awakening, the disbelief of normal humans can unravel magic, but only because their souls bear a fragment of the nothingness which stands between the sources of magic and reality.
 * In Changeling: The Lost a magical effect preys on the beliefs and psychological expectations of mortals and other supernaturals to make Changelings and Fae Tokens appear as mundane people and objects, rather than the (sometimes flagrantly) magical things they are.
 * Elsewhere in the New World of Darkness, spirits of things reflect what people believe that thing should be—a dog spirit, for instance, is nearly the platonic ideal of a dog—but it's left deliberately unclear whether this is because human belief shapes spirits, or spirits shape human belief. Is a spider spirit the way it is because we believe a spider should be this way... or do we think spiders should be this way because this is how spider spirits are?
 * In In Nomine, the Marches, the land of dreams separating the corporeal realm (Earth and the rest of the physical universe) from the celestial realm (Heaven and Hell) is populated by the power of human imagination with pagan gods and creatures of myth.
 * The Dungeons & Dragons campaign setting Planescape revolves around the idea that belief shapes the planes. It can also move mountains, as the beliefs of the inhabitants of an area determines it's actual geographic location.
 * Exploited several times in the video game Planescape: Torment; for example, the player at one point unlocks a memory of a previous incarnation who had just debated a man into the conclusion that he did not exist, which caused him to vanish.
 * The concept was added to the Forgotten Realms setting in the "Avatar trilogy" of novels. As of Third Edition, this is actually considered the default handling of gods in the default setting (Greyhawk, though they don't call it that) and Forgotten Realms; in Dragonlance, suiting the role of its gods, although belief is important to them, it's not directly necessary for their existence.
 * In Eberron, the gods exist independent of mortals entirely, but their power in the material world seems to be dependent on their worshipers - as in, the stronger churches are better able to carry out what they divine as the will of their god... though different religions don't even agree on whether or not that is even necessary. It isn't even strictly made clear that the gods actually exist, or whether the manifestations and abilities of priests and so forth are just a (local) result of their faith. And some of the things that are worshiped as gods (such as the Dreaming Dark) don't really fit any conventional use of the term.
 * The book Faiths of Eberron makes this trope even more evident. Followers of the Lord of Blades (A warforged of considerable might, but who is mortal) have access to divine magic from their belief/faith in his divinity and his cause.
 * In the 3.5 core rules, clerics were able to gain power by revering a cause. Eberron actually had attempts to train clerics of nationalism (although it failed).
 * The 2E supplement Shaman used this trope extensively, with the twist that any spirits generated by such power of belief weren't considered "real" by deities, or at least, not as "real" as the deities themselves.
 * Ravenloft, like Eberron prefers to keep its gods' legitimacy subject to doubt. At least one of the major deities of the Land of Mists, Zhakata, is expressly stated to be the figment of a crazy darklord's twisted imagination. This doesn't prevent clerics of Zhakata from receiving divine spells when they pray.
 * In Deadlands, this device works in both short and long term. When visiting the Spirit World of the setting, exactly what one sees is colored by exactly what one expects. A Protestant might see Mount Zion, with Heaven at the top and Hell at its base. A Native American might instead see a World Tree, again with pleasant things at the top and bad things at the bottom. And most of the "Abominations" in the game world are drawn straight from people's worst fears; sometimes, a house is haunted not because someone died horrifically there, but because people believe it is haunted.
 * Beyond the Supernatural features a reversal of sorts with the nega-psychic class. Most character classes in this game have psychic and/or magical abilities. The nega-psychic has psychic powers, but is so convinced that supernatural phenomena are bunk that his power is used unconsciously to suppress all psychic and magical phenomena in his area. For example, a character who can normally lift things with telekinesis will find it difficult or impossible to do so around the nega-psychic, thus bolstering the nega-psychic's belief that there is no such thing as telekinesis.
 * In Scion, the various deities (and their progeny, including the player characters) derive power from the number of people who are aware of their exploits. This is known as Legend. However, while the Gods make sure stories about them maintain circulation, they discourage outright worship, because Fate is a bastard when it comes to such strong connections. It's a dangerous balancing act.
 * Similar to the Doctor Thirteen example mentioned above, one power available to players in GURPS IOU is the advantage Mundanity. Magic and super-science fails to work in a Mundane's presence, and at the higher levels monsters, aliens and assorted other non-normal entities actually change to have mundane explanations (a monster turns into someone wearing a monster costume, the alien invasion turns into a movie set) until the character leaves the area.
 * A lesser version of this is available in the 4th edition as the perk (one-point advantage) Skeptic. Any supernatural powers the character doesn't believe in get a penalty to use, and the effect is cumulative when there are multiple skeptics present.
 * Da Orks in Warhammer 40,000 subconsciously generate a mild psychic field, its strength directly proportional to the amount of "boyz" present, so if enough Orks believe in something then reality is given a swift kick in the balls and told to follow the proper, Orky way of doing things. While it won't cause a stick to be able to shoot bullets if an Ork believes it will, Ork belief in "da red wuns go fasta" really does make vehicles painted red move slightly faster, and because Orks believe that the biggest Ork is in charge an Ork will actually grow in response to other Orks following him.
 * While Orks can't make a stick fire bullets, their powers are able to make a lot of things that shouldn't work shoot bullets. Most of their "shootaz" are little more than boxes filled with boxes that are in the general shapes of guns, and have been known to make ships without fuel fly across solar systems.
 * Tech-priests of the Adeptus Mechanicus are taught genuine mechanical skills, just in an odd and highly-ritualised way involving lots of chanting and application of holy oils in order to please the "machine spirits". Except machine spirits are quite real (semi-wetware low end AI), with many examples of a vehicle functioning long after its crew are dead, or even "going feral" and rampaging across the battlefield, so it isn't certain how much of Imperial technology is this trope and how much is genuine engineering.
 * There are also the faith-based powers of the Adeptus Sororitas (aka Sisters of Battle), particularly in Dark Heresy, where their Faith renders them immune to the negative effects of Daemonic Presence, and provides many other useful abilities at higher character ranks.
 * In Over The Edge, one NPC mentioned is a fairly obvious Expy of James Randi, who makes all the rampant weirdness of the setting shut down around him due to sheer power of disbelief.
 * Yet another White Wolf example: in Exalted, gods, ghosts, demons, and most supernatural beings (including the Exalted) regain Essence and Willpower faster if enough people pray to them. In Yu-Shan (Heaven) these prayers coalesce into Quintessence and Ambrosia, substances that are the most delicious food and drink in the history of every and are easily transmuted into... anything else, making anyone who has even small amounts fabulously wealthy.
 * This is the basic principle in which magic in Unknown Armies works. An Adept's obsession warps their view of the world so much that he can bend reality with his will simply because he is absolutely sure that what he does is possible.
 * In Shadowrun (fourth edition, at least), there are numerous magical traditions based on assorted religious and philosophical beliefs, but all are equally capable paths to studying magic. In addition, spirits take on the shape of whatever the caster believes they should take the shape of; a spirit of fire can look like everything from a triumphant archangel to a happy little puff of flame depending on who summons it.
 * In Toon, things like gravity will only work on you if you remember that it should. As a result, you can take a Smarts test hoping to fail, and if you do, you can cheerfully row across the sea with a boat that's still tied up at the dock, or make a call from a phone in the middle of the Wild West...
 * The Defictionalization of Dungeons and Discourse takes place In a World like this filled with philosophers. The upshot is that they can do things like use thier belief in cartesian dualty to do to moves in one round.
 * Genius: The Transgression features something of an inversion with Bardos. When enough people believe in something, and then suddenly stop believing (like, say, if it's publicly disproven), the energy of all those minds changing their opinion releases Mania into the world. This has created, among other things, an underground world full of dinosaurs, an army of Martian invaders, and a race of Aryan "Übermenschen" of genuinely superhuman ability.
 * The card game Munchkin Bites has an item The Yarmulke of Religious Obfuscation which gives the wearer an extra bonus against The Vampire Hunter and The Meddling Cleric.

Video Games

 * The law of physics upon which all of reality is ordered in Planescape: Torment. The game is set in the outer planes, a multiverse created from the accumulated belief of the people living in the real world (the "Prime Material Plane"), so this operates both on a grand scale (every version of Hell believed in by all of the world's cultures exists somewhere) and a smaller one (in the Planes, one can will a plant to grow or create a person by telling enough people he exists).
 * In EarthBound, the only way to beat the Big Bad Giygas is the liberal use of the "Pray" command... and the prayers of everyone who you met on your quest, culimating in the player. These prayers actually do physical damage to him.
 * A key point in the Shin Megami Tensei series, where entities from virtually every mythology ever exist, specifically because people believe in them.
 * The spinoff series Persona takes this to far greater extremes, where rumors you start actually become true.
 * The Ouendan and Elite Beat Agents series run entirely off this, in which members of a Japanese cheerleading squad (or secret government agency, in the case of EBA) show up and miraculously resolve random peoples' issues through, well, cheering and/or interpretive dance. This is taken to its logical extreme in each of their final story missions, where everyone's fighting spirit takes on a more, uh, tangible form.
 * Ouendan's
 * EBA's Bonus points for featuring the cast actually clapping their hands because they believe.
 * I WAS BOOOOOOOOOOORN IN A CROSSFIAH HURRICAAAAAAAAAAAAANE
 * Ouendan 2's
 * Final Fantasy Tactics uses this as an actual game mechanic, where characters have a numeric stat called Faith between 0 and 100, and this is directly applied to damage amounts and success rates of magic that the character uses or is hit by. A character with a Faith stat of 0 is utterly immune to magic. Characters' Faith stat can be raised or lowered with certain abilities, though if you raise faith high enough, a character will become too pious to put up with your obsession over mundane trivia like trying to stop demons from taking over the world, and will wander off to worship God in peace.
 * Used during the final boss battle of Viewtiful Joe 2. Joe and Silvia go into the real world to fight the Big Bad, but find out their powers don't work, yet his do. After getting thoroughly beaten, the crowd starts to chant their support, at which point, the two of them transform, and hand out a royal beating of their own.
 * In the PC game Black and White, the various deities gain "faith points" when humans witness them doing things; one can convert villages by building up enough faith points. Also, godly powers are driven by belief, which is gained from getting villagers to worship at your temple.
 * The Eidolon Wall in Final Fantasy IX reveals that the eidolons are in fact created by the belief of humans. The creatures of myth and legend in effect become real by people believing them, and serve as guardians of the planet.
 * So apparently they watched an episode of Transformers, leading to the creation of Ark, the Transforming Mecha eidolon.
 * In Age of Mythology and the Titans expansion, all four civilizations need their followers to do something for them before they'll grant units and upgrades. However, simply advancing your civilization gives you one free God Power to use at your discretion, so advance today!
 * In City of Heroes, the Clockwork King's robots shouldn't work at all, but because he believes they do-- thus subconsciously animating them with his telekinetic powers—they do.
 * The is the general fandom consensus towards how Silent Hill works; the Dark World and the monsters therein are manifestations of a character's fears, memories etcetera, the Malevolent Architecture is someone willing the player character not to succeed, and the player character receives weapons and ammunition from their desire to live and achieve whatever goal they're working towards. As the game continues and all people concerned become more desperate and determined, the difficulty level and the potency of available weapons increases. This also explains why the mysterious "power" is limited to the eponymous town, as only a small cult there believes in it... until the more recent games, that is.
 * The film makes this somewhat canon.
 * The main character of Okami is a severely weakened god reincarnated as a wolf. She gains experience points in the form of "faith" and grows stronger as she helps people and performs miracles.
 * Space Channel 5 Part 2. The game has people you save helping you stop evil by singing and dancing along. But the trope really comes into play
 * Subverted in Phantom Dust. It's explained in a small codex entry that Faith skils are, confusingly enough, not powered by faith, but a lack of faith. The NPC who uses the most faith skills is appropriately suicidal and self-loathing, having no faith in herself or her comrades.
 * The science-magic dichotomy in Arcanum: Of Steamworks and Magic Obscura is partially based on this; an extremely science-oriented character is immune to magic because s/he does not believe such foolishness could have any tangible effect.
 * Touhou Fuujinroku ~ Mountain of Faith works around this concept, as the Big Bad is forced to flee to Gensoukyou after the normal world loses faith in her, making her powerless.
 * While only gods need faith, belief is hugely important to the setting. Youkai (most of the cast) are created from humans ascribing the mysterious to unknown forces, and will fade away if people stop existing in them. Since this has mostly happened, the setting is behind a barrier that causes it to be sort of the opposite of the rest of the world, pulling in things that people don't believe in.
 * Many magical items in The Game of the Ages turn out to contain no intrinsic power, but your initial belief in them imbue them with actual magic.
 * How deities in Asura's Wrath gain the power of mantra.

Web Comics
""You'll also need a holy symbol to drive him back in case he's too strong for you!" "Will this can of beer work?" "Is it light beer?" "Nope." "That should do the trick.""
 * Dream Catcher does it for laughes as a bonus page FAN SUPPORT POWER BOOST!
 * In Elf Life, magic is portrayed as only having an effect on those who believe. Knowing this doesn't seem to help.
 * In Zebra Girl, magic works along these lines. As one character explains, Magic fundamentally doesn't work, but as long as you don't believe that it does. For example the main magic user tells a character to close his eyes as the magician heals him because as long as his eyes were open he wouldn't be able to accept the spell working. This same wizard then starts on a one man (but occasionally one werewolf) mission to bring back magic into the world through teaching people (mainly kids) to believe in it again. He does this as a really, really, really, good street magician.
 * The Fae kingdom in Dan and Mab's Furry Adventures works on belief, while the laws of physics take a day off. Scientist-by-heart Jyrras, then proceeds to step right through a floating platform.
 * This is the entire plot of Parallel Dementia.
 * Art from Sequential Art loses the ability to use any piece of technology, once he's told that "artists radiate an anti-technology energy... and the effect gets 100 times worse when the artist knows of the energy's existence."
 * Eventually, he has surgery to correct it, which involves hypnotic therapy, a computer chip, and a large drill.
 * Later, he tells Pip to whack him on the back of the head to disable the chip, bringing back his imaginary powers temporarily.
 * In Digger, this can have some disturbing results. In particular, street children put a new spin on a Crystal Dragon Jesus, making his mother evil. This creates a goddess so horrible that just seeing her drives a priestess insane, and apparently leaves the priestess covered in "shadows" that are not her own. The evil goddess is based on myths created and believed by street children in Miami.
 * Gods cannot die while their followers believe in them, even if they want to.
 * In The Order of the Stick, Elan creates his own god, Banjo the puppet (so called because he has a banjo) for when he multi-classes to Cleric. When Roy tells him his opinion, Elan calls for Banjo to smite Roy. A tiny storm appears and throws a tiny lightning on Roy, which has no effect. Elan comments that maybe Banjo needs more believers.
 * Played with in this Mac Hall strip.
 * In Sluggy Freelance, the following exchange takes place during the first clash with vampires:

"Howard: Excuse me. All of the women at that table would like to meet you. Dr. Minivan: A-Are you sure? How do you know? Howard: You must speak with them! Your doubt is causing them to fade away!"
 * In Fans!, the "crosses are only effective in the hands of those who believe" rule is used as an indication that a particular character's faith is wavering. In desperation, one of the fans (Rikk, a Christian whose faith had been weakening at the time) instead tries a symbol he does believe in: the Vulcan salute. It works,
 * Unwinder's Tall Comics. Here:

"Feiht: Wait... are you saying that whatever I can convince myself I can do, I can do? Dragon: Er... I have said too much already. I should go now. Maybe to another universe."
 * Legotech in Troops of Doom runs on this. If you can make an agglomeration of Legotech vaguely resembling the device you want, it will function perfectly as such.
 * Rusty and Co. has Madeline the paladin, The Ditz who purchased gardening tools as "magical weapons" from the local untrustworthy looking gnome... repeatedly. In part, because she is never ends up disappointed - if Madeline is convinced that a hoe has properties of Holy Avenger, or a spade is "vorpal halberd", in her hands the object will perform accordingly. This turns her naivete into a ridiculously strong asset. And no, it's not "she's just that good a warrior": once she was told a pitchfork is an "enchanted weapon" and decided it must be a Trident of Warning - then it actually detects "dangerous fishies and such", which allows her to discover a hidden Trap Door over pit of piranhas. She's just Crazy Awesome like this.
 * In Chasing the Sunset Fey magic is based on this. A dragon dropped in a conversation some implications, before he remembered that the other party is a pixie:


 * Fortunately for the rest of Multiverse, other Fey creatures are more sane, and pixies are too scatterbrained to remember this for long, let alone figure out on their own. Others aren't, so after this accident Leaf more than once tricked Feiht into fixing problems with magic, as he convinced her that things always were this way by exploiting a pixie's short attention span and vulnerability to Circular Reasoning.

Web Original

 * Tech Infantry borrows the explanation of the magic of Mages from the Old World of Darkness, so it follows this trope. One of the characters even tries to weaponize'' this fact of life, using a Mind Control Device to change what everyone believes about how the universe works, and thus change the way the universe actually works.
 * In docfuture's hilarious "Let's Play Sonic the Hedgehog 2 Special Edition," in Mystic Cave Zone, he points out that the game engine is belief-based, and consequently the graphics looked bad because not enough of the viewers believe that this game exists.
 * The PPC Substance Menu has this to say about Bleeprin, a medication made of bleach and aspirin: "Please refrain from reminding the PPCers that this is chemically impossible. They already know that. They don't care. However, if you remind them, it may no longer work; then they will probably kill you."
 * In Kickassia, the That Guy With The Glasses team attempted an amazing one of these to, complete with appealing to every member and many lapsed members of the site, and eventually asking the audience to join them in  . At the end of this,
 * The inverse occurs in Spoony and Linkara's review of Warrior #4, when they realize that the comics' ability to break hypertime and merge the universes is powered by their desperate attempts to believe in or discern any sort of meaning from the comics. They then call for all the critics to help them defeat the Warrior by declaring how much they…don't care.
 * Most of the monsters of The Fear Hole are created by human fears in an alternate dimension. This is mostly Played for Laughs.
 * One fan theory states that this is how Slender Man exists; the reason he scares people and gets them to keep records of him in pictures and videos is so he will exist forever.
 * I'm a Marvel And Im ADC. When Deadpool runs out of bullets he asks the audience to do this to make new bullets appear in his guns. When this doesn't work he calls the audience a bunch of amputees.
 * Gaia Online's ill-named "Demonbusters" event in 2009 ends with the titular gods depowered and turned into humans. The following Christmas event had them getting Gaians to believe and pray to them so they could become divine again.

Western Animation
"Cosgrove: ...And throw in some "Huggbees" while you're at it. Crowd: HUGGBEES!"
 * One episode of Freakazoid!! spoofs the Peter Pan example above, with Cosgrove asking the viewers to revive a defeated Freakazoid with their applause.

"Jim: ...Well? Are they clapping? Peter: A few of 'em, most of them are just changing the channel."
 * Parodied in an episode of Earthworm Jim where, after his super-suit gets stolen, Jim tries various generic ways of gaining super powers (including space radiation and radioactive arachnid bites). One of his attempts is to plead to the audience where he tells the viewer he will get powers if the audience were to "Believe! Believe and clap very hard!" prompting:

"Bender: If you don't believe in him, he can't hurt you! Santa: *smack* Bender: Oh GOD, the pain!"
 * Inverted in Teen Titans: Recently-deceased villain Slade has returned to beat the living crap out of Robin... or so Robin thinks. Turns out he'd been exposed to a drug that makes him see Slade, and his body to react as if struck. He is able to disbelieve in his opponent just in time to save himself from the killing blow.
 * In Barbie and the Diamond Castle, while a song is the key to the castle, the lyrics indicate that it's belief in the song that actually makes the castle appear. "Believe/Your song will hold the key"
 * Ember, a ghostly rocker from Danny Phantom, gets more powerful the more her fans chant her name.
 * In Aaahh Real Monsters, it was the fear and belief of monsters in the minds of humans that caused them to come into existence in the first place, and they can only exist if humans continue believing in monsters, which is why they scare. In one episode the entire cast begins to disappear because they hadn't been scaring enough humans, and reform themselves after going on a scare rampage.
 * Mocked in Futurama:


 * In South Park, the Imaginationland storyline revealed this to be the case (technically Doing In the Wizard in doing so). Everything and everyone ever imagined by someone on Earth is real in Imaginationland, including all religious figures (even including real people believed to be gods and prophets, such as Joseph Smith, founder of the Mormon faith). This is made hilarious if one remembers that Jesus has a public access television show in the real world.
 * An episode of Tiny Toon Adventures revealed that laughter (or, perhaps more correctly, the Power Of Fandom) helped cartoon characters stay young.
 * In the Christmas Episode of Buzz Lightyear of Star Command, it's the power of belief that allows Santa's sleigh to work fast enough.

Other

 * There is a joke about some Jews coming to a rabbi and asking him if he can pray for a rain. He says it won't work since they have no faith. How does he know they have no faith? They didn't bring umbrellas.
 * WE'RE GONNA YES SO HARD, WE'RE GONNA BRINK KIKI BACK TO LIFE. BELIEVE IN THE YES.
 * There's a number of urban legends about Christian college students and their Atheist professors, who try to convince their students that God isn't real. One variation has the professor hold up a piece of chalk saying that if God was real, he'd stop the chalk from breaking on the ground if he dropped it. The student prays that he will have the courage to tell the professor he believes in God. When he tells the professor this, the chalk slips out of the professor's hand, rolls down his pant leg, bounces off his shoe, and lands on the ground unharmed.
 * The professor's retort, if someone is around to say it to the original storyteller, goes something like "I've been doing this for twenty years. Either we have a coincidence, or 1/20 of a god."
 * Somewhat related: Santa Claus is often depicted as "real for those who believe."
 * A classic joke has a beautiful woman trying to drive a vampire away by brandishing her crucifix; the vampire's response is an amused, "Sorry, lady, 'svet gornisht helfen" (Yiddish for "It won't help a bit").
 * A bit odd, since it's usually the wielder's faith that counts. (Maybe she's actually a self-hating Jew?)
 * This is generally how the occult practice of chaos magic works—if someone believes in it, you, too, can believe in it, and channel it for power. Grant Morrison, being delightfully wacky, has written articles on channeling the occult significance of everything from the Greek pantheon to the New Gods to James Bond.
 * This is a common feature of New Age beliefs in general. In Wicca and some other Neo-Pagan religions, a variant is taught: you can perform magic(k) by visualizing the desired results and focusing your will upon them, but doubts in the efficacy of the technique will rob you of the necessary focus and prevent it from working.
 * Some practitioners of magic(k) claim that any symbol has the power the magic(k)ian invests in it. This can lead to two conclusions: One, the whole subjectivist interpretation (the idea of all persons living in a reality of their own making (thus not the same as the one everyone else lives in), or two, that humans actually innately possess some huge magic power, but have developed mental blocks to prevent the world's destruction by a toddler Eldritch Abomination, and such symbols are ways around these psychic walls.
 * "The Law of Attraction" and "Universal Magnetism" and "Like Attracts Like" are concepts explored in at least two books, The Science of Getting Rich by Wallace Wattles and Excuse Me, Your Life is Waiting by Lynn Grabhorn, as well as at least two films: The Secret by Rhonda Byrne (also a book) and What the Bleep by J.Z. Knight. Both films feature followers of Ramtha's School of Enlightenment in Washington State, which also teaches this concept.
 * A lot of megachurches have co-opted this by calling it "prosperity theology".
 * The Indian deity Hanuman, the "monkey god," is so caught up in his devotion to Lord Rama that he needs his followers to remind him of his own divinity for his powers not to dwindle.
 * The Logical Fallacy known as argumentum ad populum implies this. For some reason that doesn't stop people from using it, even though the implications should be obvious.

Real Life

 * The placebo effect is the real life equivalent of this, though it is far more effective in fiction than in real life. This is generally attributed to the nervous system and the immune system being interconnected, and the idea that the immune system can be activated in a specific part of the body.
 * It's pretty strong in real life too. There is one instance of rats apparently being tricked into curing themselves of a certain type of cancer by a placebo. (They were given normal water, then the real stuff in flavored water long enough to cause remission, then normal water again long enough for the cancer to cease going into remission, then flavored water without the chemo.)
 * And it's getting stronger. More recent drug trials have been seeing larger and larger parts of the placebo control group actually having positive reactions. This is mostly chalked up to people having a much stronger belief in modern medical pharmacology, and hence are more likely to believe the placebo is really a new miracle drug.
 * There's also the related nocebo effect which has been claimed as powerful enough to kill people.
 * And then things get really interesting and weird: The placebo effect can happen even when people are TOLD it's a placebo!
 * For that matter, most superstitions work this way too; believing something may encourage someone to try things and do things they might not otherwise. Like athletes who tend to have the most unusual and personalized superstitions.
 * An argument in (The Customer is) Not Always Right involves this trope when a customer seeks a blue camera and no such item exists in stock, so the manager plays along in order to get the customer to buy a red one.
 * The stock market. Expectations of the future are one of the most powerful forces, as evidenced by how stocks consistently rise/fall after optimistic/dour speeches, reports and addresses. So if the market tanks, it will come back to life if everyone just believes in it.
 * Bank runs, where people believe that their bank is failing and rush to take their money out of it, which causes more people to believe that the bank is failing, which causes more people to take their money out of it, which eventually causes the bank to actually fail, even if the original reason for thinking that that the bank was failing was completely false.
 * Really, money itself, at least the kind most of us see in our daily lives (fiat money) depends on this trope. Money gains or loses its worth only based upon widespread belief in it. Currency that could be used to buy quite a lot one day can be next to worthless the next, in the right circumstances. The money itself hasn't changed, the little squiggly world leader imprinted on it hasn't changed; its value derives entirely from how widely it is believed to have value.
 * This is how hypnotism works. You have to believe that you can be hypnotized in order for it to work, and it is impossible to be hypnotized against your will. The fact that the word "hypnotism" is applied to a half-dozen or so completely unrelated ideas, some well-understood and some utterly absurd, doesn't help.
 * In addition, even if you believe you can be hypnotized, you cannot be commanded to do things you are unwilling to do consciously. A man might be able to be hypnotized into thinking an orange is a apple, but if he believes stealing is wrong, there is no way you can force him to take money out of a wallet without permission.
 * Theoretically he can be made to believe that the wallet is his own, but this depends on the skills of the hypnotist and the susceptibility of the subject.
 * G.E. Moore's eponymous Paradox asserting that something is true demonstrates one's belief that it is true. It's kinda like screaming in a rage ("I'M NOT ANGRY!").
 * Quantum Mechanics (or a misinterpretation of it, especially the part which indicates that mere observance changes the outcome of an event), is often used as a Hand Wave for any and all of the above. However, this is not a mainstream or even accepted interpretation for quantum mechanics except for a tiny minority, and the entire point of Quantum Mechanics in the first place is that subatomic particles behave completely differently to larger matter.
 * Incidentally the reason why observation changes objects on the quantum level is that the only way to observe any subatomic particle is to collide it with another subatomic particle. It has nothing to do with consciousness changing the reality, as subatomic particles collide anyway all the time.
 * This is the most likely explanation of the Midnight Game.