Schrödinger's Gun

In a nutshell: the world of a fictional universe isn't fixed beyond what the author has revealed to the reader.

So, when faced with an impending Off the Rails event, the author can subtly tweak the facts the reader hasn't discovered yet to suit the changed plot. Improvisation masquerading as planning, if you will. For obvious reasons, this kind of plot event is pretty much impossible unless the work in question is either interactive or is written at such a scale that the author can change plot events based on what (s)he hears in the fandom.

In the former case, the advantage to this trope is obvious- a Game Master in a Tabletop Game could be badly hamstrung by a sufficiently Genre Savvy player anticipating the general direction of the campaign and being prepared for anything. The subtle Retcon this trope provides is essential to keeping things interesting. Likewise, if it's necessary for the plot in a Video Game to have the Player Character meet The Rival early on but they're technically free to go anywhere they want, this trope is essential to keeping the plot together.

The trope has also become increasingly important in more traditional fiction as of late because the Internet's technological revolution is such that an author's "twists" could easily be predicted ahead of time if enough clever fans put their heads together and talk things over. (And over.) Catching wind of this, an author might then avoid being predicted by "coalescing" Schrodinger's Gun into a sniper rifle, uzi, or rocket launcher as the situation requires. Since these cases involve more conscious improvisation, readers are more likely to consider the possibility that the writer doesn't actually know what they're doing and is just jerking them around, if not making it up entirely as they go along.

In interactive media such as video games, this trope can take the form of setting details retroactively warping themselves around the player's choices in ways that cannot be logically caused by the player character's in-universe choice -- for example, when the real location of an artifact you seek throughout the campaign is dependent on the order in which you visit its possible locations.

A helpful way to look at this is how sometimes Mystery Fiction authors will constantly feed the audience "clues" supposedly narrowing down the possible suspects, only to select the "right" clue as a Chekhov's Gunman by the denouement and fit the facts around it. Similarly, in movies it is common practice to write most of the story - and only then pick the ending that resonates the best with the test audience.

Also known as "Railshroding" (forgive the pun) because it can easily be used for Railroading purposes.

The larger principle behind Schrodinger's guns is Chandler's Law.

Not unlike the Ascended Fanon as applied to world-building.

This can be a form of Cutting Off the Branches. It May Help You on Your Quest is related, but use of this trope doesn't necessarily imply the writers themselves don't know yet what's going to happen. A fictional character taking a similar approach to their master plan is playing Xanatos Speed Chess. Contrast Retcon. See also Multiple Choice Past, where this happens when something gets different origins over a period of time and different writers.

Compare Writing by the Seat of Your Pants, Schrodinger's Suggestion Box. A subtrope is Schrodinger's Question.

See also the Useful Notes regarding Schrodingers Cat.

Comic Books

 * A Batman Choose Your Own Adventure involves the Joker deciding to kill half of Gotham's population. Batman decides that involves piping poison from a utility. The Joker is always at the first utility one chooses to investigate.
 * The villain of The DCU Crisis Crossover Armageddon 2001, the mysterious Monarch, was originally intended to be the superhero Captain Atom. After fans figured it out too soon, DC changed the story, and the Monarch wound up being a different superhero entirely. (However, the latest Monarch, villain of Countdown to Final Crisis, actually was Captain Atom (he got better). You couldn't make this stuff up.)

Film

 * Masterfully applied in the movie about the boardgame Clue. It has endings for several characters where they are the killer, and of course they Flash Back retroactively showing how only they could ever possibly be the killer. Each theatre showed it with a different ending. The Home Video showed all three straight through, and the DVD lets you do it either way, with a random ending or with all three. In the end end, !


 * The final ending is itself a parody of the game, in which the killer could win by exposing himself. Not like that.
 * the 1995 movie "Mr. Payback" had the audience vote at several points to determine how the movie proceeded.

Literature

 * Just about every Choose Your Own Adventure book does this heavily, in order to keep it interesting through multiple re-reads.
 * Rampant in the Goosebumps Choose Your Own Adventure books. There'll at the very least be a major choice near the beginning that divides the book in half (say, try to give the magic book back or try to hide it), and the entire setup, the very nature of the situation you're in, will be completely different depending on which you choose. Then other decisions will cause the same thing to happen on a smaller scale. Worst, often there'll be a situation in which you have a single decision where both lead to a quick death and an unhappy end, but the nature of what was putting you in danger is not the same depending on which you pick.
 * Chuck Palahniuk has mentioned in interviews that he got stuck at the ending of Fight Club until he read over what he had written earlier and found the line.
 * Matthew Reilly said that, in Contest, the way to kill the Karanadon - - came to him completely out of the blue.

Live Action TV

 * Battlestar Galactica Reimagined:
 * The "Helo on Caprica" plot in the first season was like this. Favorable fan reaction to Helo upgraded him to Mauve Shirt, and a new plot was born. It's actually evolved to the point of being an entire series long affair, which in retrospect the writers may have never considered until the miniseries was over and done with.
 * Likewise the four Cylons revealed in the Season 3 finale are practically Schrodinger's Hit-squad. All were perfectly plausibly human until the revelation, one even went through an "Am I a Cylon?" existential crisis and was told by an existing Cylon that he wasn't! But after the revelation, things still fit with them being Cylons. Though there are a few niggling plot details on how one managed to infiltrate colonial society for so long, the series kept its word that "anyone can be a Cylon". At this point, with one last Cylon left to reveal, the only people we know aren't Cylons are Helo  (have a Half-Human Hybrid child with a Cylon), Roslin (flat out told by the only one who knows she's not), and Apollo (can at most be a half Cylon).
 * And now with the final Cylon revealed as, the niggling details are explained.   The "oldest" among them has been explained in official statements as
 * They're still Schodinger's Hit-squad when you realize that two of the four were unplanned additions to the cast, which means that there is literally no way their reveals were planned out from the start of the show. They even had to Retcon that
 * They've since added
 * Which is one place where the writers really missed a golden opportunity to tie off some dangling plot threads by making
 * Babylon 5. During production, J. Michael Straczynski planned the B5 plot out for a 5-year arc. However, he also made plans for Real Life Writes the Plot. Indeed, the show didn't even end as he had originally meant for it to end, due to changing station commanders between seasons 1 and 2, changing several major plot points. And if you were just watching the show, you probably wouldn't have noticed (much).
 * One particular noteworthy instance of a double-Schrodinger for the same plotline. Lyta Alexander was introduced in the pilot as a telepath who got to see and have mental contact with a Vorlon, thus establishing her connection with them and providing possible material for leveling her up later. However, because the actress had other obligations Lyta didn't make it to the first season. Instead, Talia Winters was introduced, also a telepath. And she was also given a plot arc that actually began the process of leveling her up. Then, the actress playing her proved too much of a prima donna (and went through a nasty divorce from Garibaldi's actor), so she left. But they got Lyta's actress back, so they just went on and did what was originally intended.
 * The obvious actor/role substitutions: Jeffrey Sinclair/John Sheridan; Carolyn Sykes/Catherine Sakai/Anna Sheridan; Laurel Takashima/Ivanova/Lockley. Minor aversion with Ivanova, as she wasn't a straight substitution.
 * Word of God is this was done because JMS let slip that  So instead he gave that to someone else, and tossed in the occasional Red Herring regarding Ivanova for those who thought she was a straight substitution as subtle misdirection.
 * Each season of 24 has lots of shots of various characters giving significant looks and suspicious glances, so when The Mole is revealed, no matter who it is the audience has already been given a lot of seemingly suspicious behavior to justify it.
 * The reason why is that each season only starts with the first half of the season planned out. The rest is written on the fly.
 * The new Doctor Who set one of these up with the Master.
 * As a nod to the pre-written victory/concession speeches from Real Life below, The West Wing final season election had Santos' speechwriter do these, then additional permutations (won but lost home state, lost but won home state, etc.) were brought up for the contingency speech list...
 * This was done frequently in earlier seasons, too, and tied into Toby's general paranoia about counting unhatched electoral chickens. During the blowout midterm election he reveals that he has prepared a concession speech just in case. And there's a dark echo in the beginning of season 5, after . Toby is seen preparing two sets of remarks - one for use if   comes back alive and well, one for ... otherwise.
 * As a nod to the pre-written victory/concession speeches from Real Life below, The West Wing final season election had Santos' speechwriter do these, then additional permutations (won but lost home state, lost but won home state, etc.) were brought up for the contingency speech list...
 * This was done frequently in earlier seasons, too, and tied into Toby's general paranoia about counting unhatched electoral chickens. During the blowout midterm election he reveals that he has prepared a concession speech just in case. And there's a dark echo in the beginning of season 5, after . Toby is seen preparing two sets of remarks - one for use if   comes back alive and well, one for ... otherwise.
 * This was done frequently in earlier seasons, too, and tied into Toby's general paranoia about counting unhatched electoral chickens. During the blowout midterm election he reveals that he has prepared a concession speech just in case. And there's a dark echo in the beginning of season 5, after . Toby is seen preparing two sets of remarks - one for use if   comes back alive and well, one for ... otherwise.

Tabletop Games

 * A campaign example for the Tabletop Game Pokéthulhu involves the players "choosing between four houses for shelter". The book explicitly says that no matter which house the party chooses, it will be the one which contains the plot devices.
 * Included as an explicit character creation option in the Tabletop RPG FATE. When using this option, players start play with an essentially "blank" character sheet, and fill in skills as the play progresses. For example, if a character is stuck behind a locked door, the player can declare that his character has the lockpicking skill and fill it in in one of his skill slots.
 * The "Gizmo" advantage in GURPS. This advantage allows the player to be carrying around an unspecified "gizmo", which he may at any time "pull out" and declare it to be whatever device he wants it to be (that he could have reasonably possessed). Additionally, the gizmo does not "enter play" until activated, so it cannot be damaged, lost, stolen, or uncovered in a search.
 * The same is true in Toon -- Steve Jackson games love this trope.
 * This is essentially how Burning Wheel works: If you say that you want to kick a bowl of fruit into the guard's face to create a distraction, then there will be a bowl of fruit right there for you to kick. It wasn't there until you said it was. Essentially, the players all have Schrodinger's Gun, to an extent.
 * Houses of the Blooded is similar. When a player rolls for something, it's generally the right to decide things about the scene or how actions turn out. The rules explicitly state that you can decide pretty much anything that hasn't specifically been established yet.
 * There are several other games which allow the players to retroactively decide minor aspects of the current scene, such as Feng Shui and Exalted.
 * Adventure! handles this with a game mechanic: players can spend points to perform a Dramatic Edit and declare that there is e.g. a convenient manhole cover in the blind alley they've run down. This is great when the players only need to use it to collaboratively make situations more awesome, but less great when, as it sometimes does, it becomes a sort of ablative defense against railroading (why would the GM decide it was a blind alley in the first place?).
 * In Wushu, everything happens exactly as the players describe it. Additionally, the more complicated and dramatic a description is, the more dice the players receive, providing massive incentive to weave complicated and dramatic descriptions. To prevent complete insanity, actions can be vetoed by another player or the GM, and there's generally a "pool limit" maximum dice cap.
 * Nobilis has The Monarda Law, which states that the answer to a PC's question should almost never be a flat-out "no". Additionally, in that game, prophecies explicitly work by the GM throwing out a lot of meaningless symbolism -- when the PCs offer a plausible explanation, it is assumed to be true, and any action they take on it gains a bonus.
 * And really, the whole idea of it is a pretty common Game Master trick: Throw out an ambiguous scenario with a lot of plot hooks, see which one the players respond to, and run with it like it's the baton at a relay.
 * Exalted and its modern cousin Scion both rely on a Stunting system. Do it with style, and even if it is utterly ludicrous, it's more likely to succeed than if done boring-ly. For the most part, "stunts" involve pieces of the environment that the players make up as they go along. Asking if something exists in the scene should be met with "It does now."
 * The DC Heroes RPG had a similar feature. A PC may spend a few of his/her Hero Points to decree the existence of specific objects in his vicinity, if the GM agrees to allow them.
 * Then there's the Omni-Gadget, Omni-Connection, etc advantages. "Whaddya know, this 8 AP opmni-gadget in my belt is an 8 AP FORCE FIELD gadget!", or "Paradyne technologies? What luck, an old buddy of mine from college is the VP in charge of Marketing there!" and so on.
 * It is explicitly written into the rules of Paranoia that anything the GM says goes. Anything. The GM is perfectly free to roll a 5 and declare it a 17. Similarly, players may discover that they had mutations they were unaware of, that the NPC they're assigned to kill suddenly belongs to their secret society now, or that their weapon was actually sabotaged by Communists, or that while they were fleeing from a renegade robot they caused an Ultraviolet citizen a twenty minute delay in his routine. If it doesn't contradict established fact, or if the GM can invent a justification for why it doesn't, then it's all good. (Although, considering that this is Paranoia, contradicting established fact is perfectly acceptable behavior.)
 * In the new Czech RPG Střepy snů (Dreamshards), this is a mechanic given to the players -- if you want to have done something in the past that could help you in the current situation (or if you simply want something to be a certain way), you can burn one of your dream points and it's part of the game now. Hiding in a basement and the only way out is besieged by zombies? One dream point later, you can leave through the secret door (that you most certainly installed) into the tunnels below.
 * Spirit of the Century is fond of this one. The languages that a character knows need not be specified at creation. A character can spend "Fate Points" in order to make declarations about the scene in their favor or create weird coincidences (e.g. "I declare that the guard holding us hostage was my college roommate"). Players can use knowledge skills to make similar declarations (so an expert in architecture can "create" a secret passage in a building by declaring that he or she learned such in his or her research). Furthermore, numerous stunts allow for Schrödinger's Gun situations, like Personal Gadget, which gives the player a gadget less fancy than the standard, but the player can create it on the spot when he or she needs it (they had it all along), or Master of Disguise, which allows a character to effectively stop playing, then later declare that any unimportant character "is really me in disguise!" The game also gives rules for on the fly character creation, which works similar to the FATE example above -- unsurprisingly, as it's based on another version of the same system.
 * Swashbucklers of the 7 Skies and other PDQ system games are fond of this one - there's usually a power currency (Style Dice, Hero Points) to let the players declare significant facts about the game, such as inventing useful NPCs or giving them new abilities. S7S even encourages players to make flat statements that something exists and tossing a Style Die down, as opposed to asking if it's so and having to pay the cost the GM sets (though the GM should ask for more dice on particularly large changes anyway).
 * PDQ2 rules game Vox has a starting scenario to run character creation similar to a FATE game, where you choose what you can do as you need to do it until all your abilities are set.
 * PDQ2 rules game Vox has a starting scenario to run character creation similar to a FATE game, where you choose what you can do as you need to do it until all your abilities are set.

Video Games

 * Some computer games (especially Interactive Fiction, given that it is just one step away from a table-top RPG) can do this. For example, in the Peasant's Quest game, at one point, there are four bushes with a trinket hidden in one of them. No matter what order you go to the bushes, the trinket is always in the fourth bush you look in.
 * Plenty of Interactive Fiction games use this to let the player configure his character.
 * The classic Infocom game Leather Goddesses of Phobos does this, where you have to go to the bathroom, and whatever room you choose -- ladies' or men's -- ends up being the correct one.
 * A less known IF game called Enlisted pulls it off for the same reason, where you get your uniform out of a dispensing machine, and what settings you set it to (short, tall, etc), turn out to be the right ones.
 * In an even less known IF game called Amnesia the main character closes his eyes and visualizes his appearance, to check how badly he's affected by the titular condition: your choices of features turn out to be completely wrong. Dude be whack.
 * Moonmist does this with your favorite color -- which color you choose determines how your bedroom is decorated, and also (no causal relationship) who the villain is.
 * Aisle type one-move games take this to the logical extreme: you get only one move and the world need not be internally consistent since each world instance ends after that single move. For example, in the parody game Pick Up The Phone Booth and Aisle, climbing shows you to be, whereas entering the titular object reveals.
 * Some IF designers call this the Magician's Choice, and it's a very good way to turn an initially wide-open map into a small one. Whatever direction the hero goes, that's the right way to go. See Photopia, for instance.
 * Sierra Adventure Games. If the programmers can't kill your character off with something because you noticed it, they may not bother with it at all. Your car only has a fault if you don't perform the safety inspection. (Police Quest 1). The policeman's only there if you're indecent. (Leisure Suit Larry). There's only a car coming if you don't look at the street. (The Dagger of Amon Ra). The biggest example is in the latter: giving the wrong item to a speakeasy doorman would make the game Unwinnable, so it also causes a completely random person to walk in from offscreen and stab the protagonist to death. The game then quotes knife crime statistics.
 * In the horror RPG/adventure game Elvira 2 - The Jaws of Cerberus, there are three places where Elvira may be hidden. No matter in what order you reach them, the first two Elviras will be fake and transform into monsters.
 * In Fire Emblem the Sacred Stones, there's a plot choice point of which main character to follow. Excluding the main character, you get all the current secondary characters and the same new characters (with a few exceptions) appear in each chapter. Your chosen lord will even have the same encounters with the Big Bad and
 * That being said, there is a difference in the routes, at least storyline wise. In Eirika's,  In Ephram's,
 * In Seiken Densetsu 3, the player can choose three party members for the whole game: one main character and two support characters. Whoever the player picks as the main character becomes the only one who can wield the Mana Sword, and it also determines which of the three evil factions wins the race to the Holy Land, and which of the three final bosses the player ends up fighting.
 * Seen in Mario & Luigi: Superstar Saga in a boss battle at Joke's End. When Jojora asks the Mario Bros. which of her friends should come (and beat the crap out of them, presumably), the player is given the choice of four different names, which seem to refer to four different possible enemies. However, no matter which one you pick, Jojora's friend will look and fight exactly the same. The only thing your choice really affects is what name the battle display refers to her as.
 * Used extensively in Illusion of Gaia, due to Will's ability to guess any question correctly. It is demonstrated at the beginning of the game, where Will is asked to pick a card. No matter what the player picks, it is the right one. It resurfaces much later for a Wire Dilemma, where the player simply has to remember that Will is psychic and make a decision quickly. Amazingly, used at the end of the game to win a game of Russian Roulette.
 * For the Wire Dilemma, it might be subverted as
 * And for the Russian Roulette game, if you pick the wrong choice, the game ask you if you're really sure.
 * Fahrenheit (2005 video game) has a tarot card reading about half way through. No matter which card you pick or in what order, you get the same ominously creepy message. I guess You Can't Fight Fate.
 * In Tactics Ogre, there's a branching off point at the end of the first chapter of the game. You have to choose whether to kill a group of prisoners in order to frame the Big Bad. (It's complicated and political). If you choose to kill the prisoners, your best friend will reveal himself to be incredibly noble and oppose you and all governments, and throughout the game form La Résistance until you become The Atoner. If you choose not to kill the prisoners, your best friend will reveal himself to be the biggest asshole ever and side with the killers just to gain power.
 * In a way, this is a bizarre sadistic choice. You cannot be a spotless hero and at the same time have your best friend be a good guy (and alive) by the end of the game.
 * In Knights of the Old Republic II, you can answer various questions about past events, such as Revan's fate in the first game and the color of the lightsaber the Jedi Council took away from you, and the answers retroactively determine what happened.
 * As well, depending on which side you pick on Onderon, an opposing NPC will either be a mercenary or a patriot.
 * In the Star Ocean games, in order to keep some kind of weird Arbitrary Headcount Limit, you can only pick certain party members; which prevents you from getting others, who just aren't available anymore.
 * Or, in one particularly egregious case (Bowman), just not interested in traveling with you anymore.
 * Drakengard has what might be the most strenuous version of this. Depending on which ending you get the very fabric of reality functions differently. Your Dragon might be the only thing that can save the world, or you may be destined to destroy her lest she destroy the world.
 * At one point in Fable, a key is hidden in one of three books. No matter what, the key is always in the second book you pick.
 * In the second NES Chip 'n Dale Rescue Rangers game, the player faces a Wire Dilemma when defusing a bomb. Any choice turns out to be the right one, though one causes the screen to flash white with a boom, then revert back as one character says "Just kidding!"
 * The "It's War" chapter of Conkers Bad Fur Day has a pair of levers near a soldier strapped to an electric chair. The first level Conker pulls will electrocute the soldier. The second lever he pulls opens a door.
 * The Blade Runner Adventure Game had several plot points (such as whether characters were replicants or not) decided either at random in each game, or depending on the choices the player made.
 * Dead Rising:
 * At two different points in Persona 3, you can join one of three clubs. No matter which club you choose, the characters for the related social link will always be members of that club. It's most obvious with the Culture Clubs, as Yukari says Fuuka is a member of one of them, but can't remember which -- it turns out to be whichever one you end up joining.
 * To a lesser degree, the Athletic Club in Persona 4 -- you're still hanging out with Kou and Daisuke -- only difference is which one is the focus character.
 * Happens in Radical Dreamers the so-called "prototype" to Chrono Cross. Depending on which room you entered first and what you did; Magil is either a time-traveling guitar playing rockstar detective from Mars who plays with hand-puppets, the forgotten lover to Ridell, or a demon from hell. Likewise Kid is sometimes else raised by a nunnery that Lynx killed off, raised by Lynx's daughter Shea, or a gigantic berserk magic-wielding sunflower. Lynx himself is a nobleman, a ghost, a Humongous Mecha, or a giant space octopus.
 * In Riven, the passcode near the end of the game  is randomly generated the first time you see it, retroactively setting the lock to that code. It is impossible to open the lock without having first seen the passcode. This prevents a medium-aware player from saving the game early, finding out the code, loading the saved game, and then opening the lock much earlier in the game, which would have required the designers to come up with a completely different ending. (Note that the other randomly-generated passwords are not Schrödingified, so you can use this trick to unlock them ahead of time.)
 * In Cave Story, choosing to avoid speaking to an injured old man A) determines whether or not his injuries are fatal (they are only fatal if you talk to him) and also B) determines whether or not there is a vitally important rope among the junk on the floor of a room entered later, which appears to have been sealed for many years. (The rope is only there if you didn't talk to the old man.)
 * Apparently one puzzle in Space Quest 4 is about finding the two halves of a code and inputting them. Whichever order you first use to combine them is the wrong one. There's no detriment or danger, the programmers just hate you.
 * Not entirely. One half of the code is found on a wadded up piece of paper, and if you pay attention, a blob of chewing gum is covering the left side of the paper. (and therefore, the first half of the code) It should thusly follow that the second half of the code you find (later in the game) is the first half.
 * You finally bring down a Yellow Squadron bird in the "Stonehenge" mission of Ace Combat 4. No matter which one gets shot down, though, it's always  who bites it.
 * In the The Hitchhikers Guide to The Galaxy text adventure game, there are 12 or so Chekhovs Guns to collect. The bad news is you'll need one at random at the end of the game or you'll die. The other bad news is the "random" one you need is always one you don't have unless you have them all. It's a cruel game.
 * In Famous employs this to make its Sadistic Choice even worse.
 * Justified as
 * Baldur's Gate II has a sidequest where one of your companions returns home to find his sister has been murdered, and an investigation is still in progress. His father is convinced it was a hit from a rival and tells you to kill him in revenge. If you kill the rival, you later find out that he was innocent; if you spare him, he was guilty all along.
 * In Tales of Symphonia Dawn of the New World, Emil is asked to guess which of Lloyd's companions joined him at the end of Tales of Symphonia. Since it was based on Relationship Values there, any answer could be a correct one, and, indeed, no matter what Emil (that is, the player) guesses, Lloyd admits that he guessed correctly.
 * In Batman: Arkham Asylum, at one point Batman must search three body bags in order to continue. No matter what order he opens the actual bags in, the result is always the same.  Also, no matter what order you collect the audio logs in, they are always the next in the set, as are the Spirit of Arkham messages.
 * An experience while playing Deja Vu seemed like a literal Schrodinger's Gun: trying to shoot the gun-toting mugger resulted in him firing first for a game over. Restarting and giving in to his demands the next time around let him escape while claiming that the gun wasn't even loaded.
 * Of course that could just be the mugger kicking you when you're down.
 * In Dragon Age: Origins you may end up with plot relevant fights halfway through traveling, no matter where you are, and there are dozens of them. Even if you meet a bunch of elves defending themself against some darkspawn in the far northwest near the dwarven home, while the elven woods are southeast and the darkspawn isn't actually rare on the surface that far north.
 * The origin stories always end with Duncan bailing your ass out of trouble, which every origin you choose will be the place Duncan decided to recruit a new Grey Warden. It is implied if you go back to those places as a different origin that what happened happened but without Duncan saving that would-be hero. The Dwarven Noble, the second child of King Endrin, was framed for murdering his brother and killed on the Deep Roads; the Dwarven Commoner died in jail, refusing to eat; the human noble was killed by Tim Curry, etc.
 * Awakening is an aversion if you don't import a Warden; there is a default outcome for everything that the Orlesian Warden Commander will arrive to (Alistair is  etc.)
 * Assassin's Creed II does this with The Truth. No matter what order you find the glyphs, the segments of the video and puzzles will always be found in the same order.
 * A plausible explanation is that subject 13 shares the same memories of Ezio's travels, and subsequently knew in what order you'd visit the places he marked for the pieces of The Truth.
 * Averted in Heavy Rain. The eventual set of reveals rely heavily on fourth-wall shenanigans and mess with the player's expectations from the standpoint of someone playing a game as much as from the plot itself similar to Knights of the Old Republic II, so it's likely that this was a deliberate decision intended to give more value to the first playthrough.
 * In the FMV-based adventure game Ripper by Take 2 Interactive, the titular serial murderer has four possible identities, depending on how the player pursue the investigation.
 * At the end of The King of Fighters '95, returning villain Rugal announces his plan to destroy your team for foiling his plans last time. At the end of The King of Fighters '96, Chizuru reveals that she lured your team there because she needed the help of those responsible for defeating Rugal. In both cases, this speech is made regardless of which team you are playing, and whether or not they actually won or were even in the previous game. (Aside from Geese/Wolfgang/Big, whom even she refuses to acknowledge.)
 * A quest in Guild Wars requires the player to help the prince find a gift for his beloved. There are three items you can show him; the first two will always be rejected, no matter the order you try them in. An alternative option is to find only one of the items and hand it directly to the birthday girl, who gets pissed that the prince hired someone else to choose a gift for her.
 * Guild Wars 2 makes extensive use of this trope, from personal storylines (which affect instances) to dynamic events (which alters the state of the world players share). An example of the latter is a village besieged by centaurs: if players kill the centuars, villagers will come out of hiding and offer services to anyone who visits; if nobody bothers to fight off the centuars, the village will be overrun and turned into a centaur fortress.
 * The Master Sword in the Legend of Zelda Oracle games can come from two conflicting sources depending on which game you play first.
 * The games also include a Schrodinger area of the game map: at a certain point in the game, you can earn a flute that will eventually allow you to summon one of the three animal companions. Each of them have skills that allow you to reach places Link can't reach alone, and depending on which flute you get, part of the map ends up being an area that requires that companion to get through.
 * Late in Skyward Sword, Link must revisit each of the previous areas in order to collect the parts of the Song of Heroes. These can be done in any order, but no matter when you choose to do Eldin Volcano you always arrive just as it erupts.
 * In Contra: Hard Corps, Colonel Bahamut's plan for the Alien Cell depends on which path you take through the game.
 * From the same game, Bahamut's base is either right next to your current location, a train ride away in the jungle, or a boat ride away on an island.
 * In Dawn of War II: Chaos Rising there is a traitor in your party. And you really don't know who it is. The choice is only fixed if . But really,   is the last person you want as a traitor..
 * Each Mass Effect game has an instance in the beginning; regardless of what Shepard's background and military reputation are, he or she is the perfect candidate for the first human Spectre. Likewise, when Mass Effect 2 begins, regardless of whether the imported save file flags the council as saved, lost, or lost and replaced with an all-human council, Shepard "did everything right."
 * Justified in the latter case, as no matter the outcome, it is perfect for Cerberus. Although the degree and specifics of it vary, any of the endings puts humanity in an unprecedented position of power and influence, which is exactly what Cerberus wants.
 * In the end of Metal Gear Solid 3 Snake Eater, you  No mater what you choose,
 * Which is odd as
 * In the FMV game Terror T.R.A.X. - Track of the Vampire (played by Spoony here, one of the Bad Ending paths has one of your agents getting captured by a Mad Scientist vampire. When the second agent finds the first, Mission Control orders her to shoot him preemptively. If you don't, he springs up as a vampire and kills the other agent. If you do, the vampire calls to taunt you with the fact that the agent was still human so you killed him needlessly.
 * Done several times in Portal 2, with an actual gun. With some of the puzzles, the player needs to fire the portal gun quickly to not die, but if they fire the wrong portal, they end up dying anyway. To fix this, the programmers fixed it so that whichever portal you fire is the right one and it retroactively changes the portal you had already placed.
 * In XIII, the player must enter a locked cabin to obtain a fuse. There are several guards in the area, but the last one who gets killed is always the one holding the key.
 * In Dragon Quest V, it doesn't matter whether you decide to marry Bianca or Nera, either one will turn out to be . The original game plays this straight, but the remake justifies it a little. The new character Debora is Nera's sister, so they share the same fate,.
 * In Catherine, the differences between the "Bad", "Good", and "True" version of each ending are supposedly determined by how well the girl can sense your feelings (that is, your position on the Karma Meter), but other events happen differently seemingly independently of your feelings about relationships.
 * Deus Ex Human Revolution has this at least on an occasion: when you rescue, the third one will always have the , regardless of the order you visit them.
 * Starcraft II includes three levels where you can choose one of two possible methods to take. While two aren't one of these (merely determining if you strip the Zerg of their primary Zerg Rush generating unit or of their flying units), one is. In the Colonists story arc, the climax is to either fight off the Protoss to try and see if the Zerg infection amongst the colonists can be arrested and perhaps cured, or to side with the Protoss and mercilessly burn out all of the infected. Choose the former, and the game reveals that there were only a few infected colonists, who are easily contained, and Dr. Hanson leaves the ship to work on researching a cure. Choose the latter, the infestation is far more widespread, and Dr. Hanson goes insane and infects herself, turning into a monstrous human/zerg hybrid that Raynor has to kill.
 * Used extensively by Silent Hill: Shattered Memories, primarily for purposes of Mind Screw.
 * In Fear Effect, two of the player characters continuously are at odds over whether or not a girl they are helping is a legitimate damsel in distress or secretly the Big Bad playing a Xanatos Gambit. Right before the final battle the player must decide who is correct and that choice will determine the final scene of the game. If the player decides innocent it will turn out she is innocent, if the player decides she is lying it will turn out she has been lying throughout the whole game. So in essence the girl is paradoxically telling the truth AND lying throughout the story until the scene when the player makes their decision.
 * In Grand Theft Auto Vice City, the player is recruited by an old Haitian woman to help out her son in an upcoming gang war. This mission involves assisting a group of a dozen Haitians as they fight off wave after wave of Cubans. This raises the question of exactly which of the dozen Haitians is the son you are trying to protect, as mechanically and graphically they are all identical. However, the mission is a failure only if ALL the Haitians die, which means that 11 of the 12 are "expendable", i.e. NOT the son you're supposed to protect. Thus one can conclude that the son will always be the final Haitian killed, regardless of the order in which the Haitians go down.
 * Brain Lord: In the first town, there's a small sidequest you can do involving rescuing a pair of kids who wander down into a cave below the city. However, they only get lost in the cave if you actually talk to them - ignoring them or simply not talking to them will mean you don't need to rescue them.
 * Escape Velocity Nova has a few - mainly, the fact that you with little doubt is the universe incarnate in two of the storylines, certainly isn't in one of the storylines, and has some question-marks regarding that status in the remaining three storylines. Other than that,  either set up   or is , and someone shows up in the Auroran storyline that has what would have been your role and backstory in the Pirate storyline.

Web Comics

 * The idea is brought up in this Irregular Webcomic strip. Fittingly enough, the characters are players in a Deep-Immersion Gaming RPG, and they actually mention Schrödinger.
 * Not only does the trope appear in that particular strip, but also in the writing process behind the strip. In the earlier draft of the comic, David Morgan-Mar kept flip-flopping on whether the punchline should reference Heisenberg or Schrödinger. He decided on Heisenberg and wrote a long note below the comic, explaining Heisenberg and the Uncertainty Principle, before realizing that Schrödinger worked better as a punchline and changing it. He left the note below mostly unchanged, presumably as a record of the uncertainty in the writing process.
 * Also appears in Darths and Droids by the same creator, starting here. It also appears in a more amusing variation, Schrodinger's Bodyguard, seen here.
 * In "Chainmail Bikini: The Nightmarish Legend of Deuse Baaj", the players are sent to retrieve a farmer's pigs in return for a sword. Instead of fighting the goblins that have stolen the pigs, they set a siege and wait until the goblins have run out of food and surrender, thus totally ruining the adventure the GM had written. (And then they go and slaughter the goblins anyway.) The GM gets back at them by having the farmer's village been attacked and razed by the minions of the Big Bad Diabolical Mastermind by the time the characters return.
 * Not to mention, a player thoughtlessly wonders why the starving goblins didn't simply eat the stolen pigs; at which point the rescued pigs suddenly transform into a pile of bones as the gamemaster quickly retcons the situation.
 * In the sort-of prequel DM of the Rings, during a dice roll for an enemy attack, the dice accidentally drops beneath the table to an inconvenient spot. The player who the attack was targeted towards then calls himself an "Uncertainty Lich" between life and death (though the issue is quickly cleared up).
 * Hilariously occurred in Gold Digger Tangent. The comic had a forum right beneath it, where people often speculated. One person yelled out, without spoiler tags. "Ooh! That one guy we saw taking a bath is going to swoop in and pull a Big Damn Heroes, making him a Chekhov's gun!" The artist's response? "Great, now I need a new way to bail them out!" He figured it out.
 * In Chapter 2 of Gunnerkrigg Court, a set of glowing pictures (a Shout-Out to the film The Peanut Butter Solution) are briefly featured in the library. When asked about the pictures, Tom Siddell explained that he has planned out a Story Arc involving those pictures, but he isn't certain that he'll be able to work that arc into the comic. So it's unknown at this time whether those pictures will end up being a Chekhov's Gun or just Cow Tools.
 * The waveform has collapsed: Tom says that particular story arc has been cut.
 * Every single thing in MS Paint Adventures. Since the various series use fan-submitted suggestions to drive much of the plot, seemingly non-sequitur commands like "Build a fort out of your desk" can lead to larger developments in the in-game universe. Or just be one-off non-sequiter gags.
 * This even holds true in the current storyline, Homestuck. Although Hussie has officially closed the suggestion boxes, and they won't be opened again until Homestuck is over and the next story has begun, he's taking cues from the fans; he's said that "ninety percent of 'calling it' is actually suggesting it in disguise."
 * Also used in-story in Homestuck:
 * If somebody who read through Bob and George somehow managed to be oblivious to the heavy Leaning on the Fourth Wall, they might get the impression that the comic had a complex, carefully planned, intricately connected plot. However, by his own admission, Dave was just really good at making crap up on the fly, and then making up more crap to explain why the previous crap was significant.
 * Tim points out that Steve is using this technique in chapter two of Loaded Dice.
 * In Questionable Content, Faye once found a box of condoms in the couch. Marten says it's Pintsize's, and Pintsize says it's not his. The author's notes at the bottom read: "So who does the box in question belong to? [...] I haven't decided yet."
 * Used in this Something Positive.

Web Original

 * In The Spoony Experiment's Let's Play of the FMV game Phantasmagoria2, Spoony mocks how the game tries to get around this--that the protagonist Curtis could experience the various supernatural death threats in a different order--by having him seem newly surprised in each clip, as though every one was the first (which it could be, depending on what the player does). In the finale of the Let's Play,.

Western Animation

 * The Season Two premiere of The Venture Brothers is a veritable Schrodinger's machine gun. The writers deliberately took all the fan speculation about how the cliffhanger at the end of the Season One finale would be resolved, and made it all true. A partial list follows.
 * Total Drama has an alternate ending each season where the runner-up (in slightly different circumstances) actually won the prize. In fact, for the second season, it was declared that both endings were the possible "real ending", since each country voted differently on which of that final two they wanted to win. Unfortunately, the first and third season endings ended up very contrived by comparison.
 * My Little Pony Friendship Is Magic is a veritable font of minor Shrodingers Guns (Schrodinger's Derringers if you will), with all manner of nods towards it's unexpected older fanbase. The most obvious is Derpy Hooves, who was an animator's joke in the first episode, but started getting inserted into episodes after the creators noticed the internet had latched onto her, and has even recently had a (rather controversial) voiced appearance.
 * Total Drama has an alternate ending each season where the runner-up (in slightly different circumstances) actually won the prize. In fact, for the second season, it was declared that both endings were the possible "real ending", since each country voted differently on which of that final two they wanted to win. Unfortunately, the first and third season endings ended up very contrived by comparison.
 * My Little Pony Friendship Is Magic is a veritable font of minor Shrodingers Guns (Schrodinger's Derringers if you will), with all manner of nods towards it's unexpected older fanbase. The most obvious is Derpy Hooves, who was an animator's joke in the first episode, but started getting inserted into episodes after the creators noticed the internet had latched onto her, and has even recently had a (rather controversial) voiced appearance.
 * Total Drama has an alternate ending each season where the runner-up (in slightly different circumstances) actually won the prize. In fact, for the second season, it was declared that both endings were the possible "real ending", since each country voted differently on which of that final two they wanted to win. Unfortunately, the first and third season endings ended up very contrived by comparison.
 * My Little Pony Friendship Is Magic is a veritable font of minor Shrodingers Guns (Schrodinger's Derringers if you will), with all manner of nods towards it's unexpected older fanbase. The most obvious is Derpy Hooves, who was an animator's joke in the first episode, but started getting inserted into episodes after the creators noticed the internet had latched onto her, and has even recently had a (rather controversial) voiced appearance.

Real Life

 * Many of a stage magician's illusions rely on some form of this. The Other Wiki has more details.
 * Politicians facing elections usually have their victory and concession speeches prepared well in advance. Similarly, newspapers pre-write articles and obituaries. Hilarity Ensues if they jump the gun and publish a wrong article.
 * The West Wing, being a show about politicians and elections, mentioned this.
 * Similarly, Nixon had a speech ready in case something happened to Neil Armstrong and crew during their lunar soujourn.
 * The items (from newspapers with banner headlines to caps and T-shirts) that get waved around during post-game celebrations at the Super Bowl, World Series, and other championship sports events featuring the team that was just victorious seconds earlier were also prepared in advance in versions for both teams. The merchandise items proclaiming victory for the losing team are often sold to third-world countries that don't care who really won as long as they get proper clothing.
 * To avoid a portrait subject having to spend weeks sitting still, portrait painters used to do a subject's body, clothing, and furniture before the customer actually paid for a picture. Then they'd just add on the appropriate head (which is why some portrait figures have oddly long necks).
 * The creators of South Park create each episode within six days in order to keep turnaround times for major events and trends quick and stay as current as possible. In fact, during the 2008 Presidential Election they were able to air an episode featuring  because they had actually prepared an episode for either eventuality.
 * Not quite true. This their original intent, but as time wound down, they found that storyboarding, writing, and animating both possibilities and have it play coherently was too much of a pain, so they said, "to hell with this," and animated the episode shown,
 * Reportedly, General Eisenhower late in 1944 found a note in his jacket pocket which was the speech he had written regarding the failure of Operation Overlord (i.e. the Normandy Invasion).
 * The November 5, 1996 (US election day) New York Times crossword puzzle had two seven-letter words with the clue "Lead story in tomorrow's newspaper (!)" - which could be answered with either "CLINTON ELECTED" or "BOBDOLE ELECTED." The seven down words crossing the first word worked with either set of letters; for example, the clue for the word crossing the first letter was "Black Halloween animal," which could be either BAT or CAT. More details.

Theater

 * A musical based on The Mystery of Edwin Drood stops the action at the point where Charles Dickens' death left the novel unfinished and then uses audience votes to determine the villain, lovers and true identity of Dick Datchery.