You Already Changed the Past

"Things have their shape in time, not space alone. Some marble blocks have statues within them, embedded in their future... Any moment now, Janey's watchband will break. Somewhere, the fat man is already lumbering toward the shooting gallery, steps heavy with unwitting destiny."

- Dr. Manhattan

"One of the major problems encountered in time travel is not...about changing the course of history - the course of history does not change because it all fits together like a jigsaw. All the important changes have happened before the things they were supposed to change and it all sorts itself out in the end. The major problem is quite simply one of grammar."

- Douglas Adams, The Hitchhikers Guide to The Galaxy

You go back in time to Set Right What Once Went Wrong, only to discover that the "changes" you're making to the past were what "already" happened anyway. In other words, there was no "first time around" - the past only happened once, there were no different "versions" of it, and the changes you made to the past ultimately created the very past you read about in the history books before leaving on the trip.

It's like being Time's own personal Unwitting Pawn.

This does not necessarily mean that You Can't Fight Fate. For example, if Bob wanted to go back in time to stop Alice's death, he could simply convince his past self that Alice still died in the future. Following this logic, Alice never dies at all -- and Bob suddenly remembers how several months ago, some "other" Bob came up to him insisting that Alice was going to die of something and the two of them had to go save her, which they did, so she's still very much alive and well all along. (Do you have a headache yet?) Or to avoid the headache and ensuing paradox, Future Bob could go back and save Alice in such a way that Past Bob still thinks that she died.

Needless to add, grammar can sometimes become thoroughly useless at trying to put the point across, as all sense of tense gets thrown of the window. This trope is easier to observe rather than analyze.

Note that You Already Changed the Past implies Only One Possible Future, which is the version of fatalism found in many older works, such as Greek Drama, that don't involve time travel.

This trope arguably makes the most sense when considering time travel from a scientific point of view, see the Novikov self-consistency principle. However, the number of time-travel plots that it allows for are extremely limited and the logic gets complicated very quickly. This, however, also has the side-effect of creating a 'self-correcting universe' usually by a slew of Contrived Coincidences (ie. if you try to shoot your grandfather the gun will jam; if you try poisoning him he will recover; if you try strangling him you will be overcome; if you wear Power Armor from the future you will have second thoughts; if you try sending a bomb back through time and detonating it directly inside his chest the time machine will break down). This can also lead to a scenario where the only reason why the past is not changed is because someone else says 'you cannot' and you take his advice. Meaning the advice itself is a part of the universe's self-correcting nature.

Thus, most time travel stories that involve altering the past will provide some of the characters with Ripple Effect Proof Memory. This makes less sense, but it makes for a narrative convenience. If a You Already Changed The Past plot is used, the time travel will probably be a one-off thing, since repeating it would most likely get tedious.

The Ancient Greeks and Vikings loved the notion that You Cannot Change the Future, and their works heavily imply that they believed in this specific notion of time (which even the Gods were trapped in). Although they used predictions rather than time travel, the effect is the same. Many first-time readers of the classics who don't buy into this notion of time, or don't realize this is why You Can't Fight Fate in the classics, have a hard time accepting The Fatalist behavior of classical Greek and European heroes.

See also Self Fulfilling Prophecy. Compare Retroactive Preparation, where having changed the past already works to your favor. Related to Stable Time Loop where you go back in time, because you already changed the past.

Examples:

Anime and Manga

 * Urusei Yatsura has time travel in a few occasions.
 * In one, Lum goes into the future where she brings back Ataru's diary. He reads it and believes things will go right for him, but attempting to cause them makes everything go horribly wrong. It's later found that when writing the entry about everything that went wrong, his tears blur the ink, causing it to look like he wrote about things going well.
 * In the other, the cast goes back in time to prevent Mendo from getting claustrophobia and nyctophobia. As a result, young Mendo pisses off the modern Mendo, causing him to attack his younger self. While hiding from his older self, young Mendo was trapped in a dark jar, causing him to grow deathly afraid of dark and tight spaces.
 * Tsubasa Reservoir Chronicle. Details would be massive spoilers, but suffice to say that time travels differently in different universes, and something the heroes do midway through in a world that later turns out to be their own past sets up the very premise of the story, as revealed in the finale.
 * Also, one character who In fact, depending on which angle you see it from, the whole story wouldn't have happened if the past had not already included the influence of the future.
 * However, the first instance of tinkering with time that we knew of was not an example of this - the group visits the world of Shara twice, before and after visiting Shura which turns out to be the past of Shara; and the effects of their actions are quite visible. CLAMP seems to have lost track of their time-travelling system as the Mind Screw got more and more complicated...
 * In Rave Master, after much time is spent freaking out over what horrible ways they've twisted the past, Sieg, Elie, and Haru (but mostly Sieg) discover that
 * Steins Gate: Understanding this concept is what allows  His early episodes boast about being "able to cheat the universe itself" doesn't look so silly anymore by the end.

Comic Books

 * A Blade series had Doctor Doom lure the Daywalker to his castle, where Doom then proposed Blade with going back in time and saving his mother from a vampire attack. Blade asked him why he should do it, and Doom replies with "Because I've already seen you do it in the past." Doom is nice enough to give him a serum which would suppress his bloodthirst though.
 * An issue in The Mighty Thor series had an storyline where

Film

 * Twelve Monkeys, as well as its inspiration, La Jetée.
 * The Terminator gives a rare example of the good guys directly benefiting from the immutability of time. The machines sent back a Terminator to kill Sarah Connor before her son John Connor was born, in response, the rebels send back... the guy who becomes John's father.
 * Also, in a deleted scene, it turns out that Cyberdyne, the company that built Sky Net and the original Terminators, acquired the remains of the Terminator. The sequel shows that they'd begun reverse engineering the Terminator, which would presumably have led to the creation of the Terminators had the events of the sequel not occurred, so it happened on both sides.
 * Harve Bennett's explanation for why the Enterprise crew was so careless about altering history in Star Trek IV the Voyage Home seems to be (he says it in a rather disjointed way) that this trope is in place and the characters are Genre Savvy. Although this contradicts how time travel is usually portrayed in the series, it does fall into line with the one episode of the original series that also used the "slingshot around the Sun to visit 20th century Earth" method.
 * In the reboot movie Star Trek, 200-something years in the future,
 * This movie runs on the parallel-universe model of time travel.
 * But the problem with that theory is that
 * Nero came from the Prime universe, So, there would be three time branches: the Prime Universe (Original Star Trek), the Rebooted Universe (Star Trek 2009, diverging from the encounter of the Narada with USS Kelvin, where ) and the Re-rebooted Universe (diverging from the unknown person arrives from the future to some point between the USS Kelvin's destruction and ).
 * This gets covered regarding the movie Happy Accidents very well here.
 * This is a central theme of brilliant Spainish Mystery thriller Timecrimes.
 * In Deja Vu, the first few attempts at actually changing the past just end up causing things the characters and audience have already seen happen.
 * This could be a case of
 * An interesting case is the movie Paycheck. What happens to the protagonist (he is administered a procedure which would erase all of his memories from the coming two years; when he is finished, he's told these two years already happened) would be a perfect example of this trope. Only there's no time travel (though the plot revolves around a future-seeing machine).
 * In the 2007 film Premonition, Sandra Bullock lives the week of her husband's death out of order.
 * Played with in Back to The Future, where Marty goes back in time and introduces 1985 concepts to 1955, but the movie implies that he only changes the source of the original idea without actually altering their progression into the modern day. He didn't invent skateboards but he introduced skateboarding to Hill Valley earlier than would have caught on naturally, and he didn't write Johnny B. Goode, but hearing his guitar solo inspired Chuck Berry over the phone. Since these things don't actually change the future, it looks like they were always that way.
 * One of the signs that Bill and Ted are clever if not book smart is their recognition of this trope; they realize that to solve a problem in the present, they can use their time machine to plant helpful items in the past, and then they'll be there for their present selves to discover - and they keep reminding each other "Once this is over, we have to go back and place all that stuff!"
 * In fact, the entire climax of the second movie is B&T and the Big Bad performing dueling versions of this.

Literature

 * There Will Be Time by Poul Anderson. A substantial number of humans have had the innate ability to Time Travel since before recorded history (possibly because it was inserted into the genome by future travelers). So little of human history is known exactly, and the book's scope is so great (from Jesus' crucifixion to a far-future postapocalyptic revival of civilization--at least) that the inability to change the past comes up only rarely--but the protagonist is nearly broken.
 * It is established fairly early in the story that it is impossible to change anything that the hero knows about what will happen. Every attempt he makes to save his father (who died in WW-II) is prevented in some way.
 * Eoin Colfer's Artemis Fowl Time Paradox
 * Diana Gabaldon's Outlander series runs into this a lot.
 * The Door Into Summer, by Robert A. Heinlein. Various instances of Human Popsicle, but more importantly a weird time machine that has an equal chance of throwing the subject forward or backward. The protagonist uses it knowing he HAS to be sent backwards. Bonus points to a throwaway gag that suggests that Leonardo da Vinci is (and always has been) an accidental time-traveler.
 * His short All You Zombies involves a time agent making sure he completes the correct steps to finish the changes he remembers happening earlier in his life.
 * In Aunt Maria, by Diana Wynne Jones, the main characters go back in time
 * Technically
 * Dragonriders of Pern
 * In Dragonflight, F'nor returns from the past to warn his friends that an expedition they're planning is going to fail. Unfortunately they now know that if they don't go it'll create a paradox because the guy who warned them won't come back in time to warn them... so his warning has exactly the opposite effect. Knowing they're going to fail they have to set out anyway.
 * And of course we have the situation where there are too few riders in the present due to many of them having suddenly disappeared in the past. So someone travels into the past to gather some more, thus causing the shortage. (Although it's not as futile as it sounds because their numbers would have declined anyway due to a coming period of long inactivity. This way their disappearance is useful.)
 * This is without even mentioning events from a more recent novel in which a Gold somehow randomly jumps to a few centuries in the past after being given a BAD mixture of gene-altering medicines in an effort to cure a plague running through the dragons themselves, which results in said Gold crash-landing in a time when one of the last trained geneticists is still alive, thereby resulting in the creation of aforementioned medicines when they would not have otherwise been made, but had already been made anyway because in the past the sick dragon had already crashed....good god my head hurts.
 * And even THAT ties back to the original trilogy of books by establishing, at long last, just what the 'Ancient-timers' room was made for, and what the colorful diagrams REALLY were.
 * Also noteworthy is the climax of All the Weyrs of Pern, where the AIVAS reveals to Jaxom that . Of course, if those hadn't occurred, none of the events of those books would have occurred either, including the discovery of the AIVAS itself.
 * Tim Powers plays with this trope a lot in The Anubis Gates. The time-traveling protagonist comes to believe that You Can't Fight Fate, then learns that it's not that simple, since historians don't know all the details.
 * He encounters the brand-new original manuscript of a poem he'd studied in his own century, and wonders how it would pick up the stains he'd seen on it in his own time. A poet he recently met then walks in carrying some food, puts it down, and picks up the manuscript with his greasy hands to look it over.
 * He encounters a 17th century book with an inscription in it that shakes him up. He later travels accidentally to that century, and on encountering the then-new book, writes the pig-Latin inscription addressed to himself that he would read in the future.
 * The climax of Harry Potter and The Prisoner of Azkaban. They go to the past to save Buckbeak and Sirius, and Harry wants to see a mysterious figure that he believes to be his father.
 * To Say Nothing of the Dog by Connie Willis involves time traveling historians (which first appeared in her Doomsday Book)who spend a lot of effort to repair the "incongruity" caused when one of them inadvertently brings a cat forward from Victorian England (they're extinct in 2057). This involves trying to make sure that the cat's owner winds up with the "Mr. C" that her diary specifies after they've accidentally introduced her to a different man.
 * Blackout and All Clear, also by Connie Willis, have a similar example. Some historians go back to WWII era, then find that they can't get home. They agonize over every little thing they do, worried that the slightest change might cause the Germans to win the war.
 * Time Travel in the Pliocene Exile novels works this way. Of course, since Time Travel must take you back six million years (and then only works in one spot in France), it's rather difficult to know exactly what the time travelers already did.
 * Used extensively in Suzumiya Haruhi this seems to be the whole purpose of future(er) Asahina. Who is suspected to be the superior of Present(or rather not-so-future) Asahina, and puts her younger self trough all the missions and trouble she already went trough herself. So she already changed the past because she will order herself to go to the past and change it so she can get to the future and order herself to change the past.
 * Minor example in So You Want To Be A Wizard by Diane Duane: Nita and Kit are stopped for a moment on their way to a world gate by a loud bang on the other side of a door they are about to open. It turns out at the end of the book.
 * This was true in the novel The Time Travelers Wife by Audrey Niffenegger. The main character was constantly going into both the past and future, but everything was pre-set. Everything he did when he went into the past, he had "already done", and once something happened, he could never change it; in situations where he already knew what was going to happen, he had to act in the way he had already acted, he didn't have any choice.
 * Douglas Adams' The Hitchhikers Guide to The Galaxy universe works this way. in the second book, The Hitchhikers Guide to The Galaxy]], while stranded on prehistoric Earth with an exodus' worth of incompetent aliens who are plainly going to begin colonizing, Ford Prefect tells Arthur Dent "This doesn't change the past, this is the past."
 * Isaac Asimov's short story "The Red Queen's Race" has a character who tries to make this trope happen.
 * Specifically,
 * Unborn Tomorrow, a short story by Dallas McCord Reynolds. A wealthy man wants a private eye to locate a time traveler from the future and get the secret of eternal life. He believes such time travellers would go to the Oktoberfest, where everyone would be too drunk to notice anything strange about them. The secretary is surprised when her boss curtly turns down this chance to get drunk on someone else's money. The private eye explains that he's already taken the assignment three times, and each time the time travelers sent him back to this point in the time line, with a massive hangover from drinking too much German beer. There's no way he's getting another hangover piled on top of the previous three, not for any amount of money!
 * The Skull by Philip K Dick. An assassin is sent back in time to kill the founder of a subversive religion before he gives a famous speech, only to realize that the Founder is himself -- the 'miracle' that inspired the religion's creation was him appearing after he'd been killed (he'd arrived at the wrong point in time) thus 'coming back from the dead'. The Rousing Speech supposedly given by the Founder never actually happened, but was a result of history being embellished after his death.
 * An interesting example in The Redemption of Christopher Columbus by Orson Scott Card. The book takes place in an technologically-advanced, but dying, Earth and the protagonists are trying to find at which point in history they need to change events. While researching Christopher Columbus, they find that a vision he wrote about in his diaries was actually a hologrammatic projection sent from a parallel future to their own.
 * Happens quite a lot in Count and Countess, in which the two eponymous characters exchange letters with each other despite living more than a hundred years apart. Notably, Elizabeth, living in the 1500s, knows that her ancestor Matyas Hunyadi (in the 1400s) held the throne of Hungary for a very long time. In an attempt to save Vlad Dracula's life, she warns him not to try to make a grab for the throne, or he will probably be killed. As a result, Vlad stays as far away from Hunyadi as possible.

Live Action TV

 * Star Trek the Original Series ("Assignment Earth")
 * Early seasons of Andromeda used this, but it degenerated into Timey Wimey Ball territory after a while.
 * The first Time Travel episode of Stargate SG-1 ("1969") can be perceived as following this logic, but none of the subsequent Time Travel episodes in the Stargate Verse can -- they all involve alternate timelines instead.
 * Though it seems SG-1 held to the "Alternate timelines/universes" first. The 20th episode of Season 1 had the "Quantum Mirror" which put Daniel Jackson in an alternate timeline/universe. "1969" was the 21st episode of Season 2.
 * Stargate Continuum shows the present universe being erased by Baal's actions in the past. As a part of the SG-1 team consciously try to outrun the phenomenon, the stargate wormhole somehow shields them from it. So, while there are alternate realities in the Stargate Verse, those may be unrelated to time travel. Either that, or the writers just can't decide.
 * In the Murder Most Horrid episode "A Determined Woman", a female scientist working on a time machine becomes so frustrated with her idiot husband's antics that she kills him. Several years later she is released from prison, finishes her time machine and goes back to try and save her husband, only to find that his confusion between the two versions of her is what caused his erratic behavior in the first place.
 * After Hobgoblins, a film, was shown on Mystery Science Theater 3000, Tom Servo tried to go back in time to stop the movie from being made by hunting down the director and... kicking him in the shin. Upon Tom's return to his present, Crow pulls up an article where the director claimed that his inspiration for Hobgoblins was that time when a squat red robot ran up to him out of the blue and kicked him in the shin...
 * In the Hercules: The Legendary Journeys two part adventure "Armageddon Now", Callisto goes back in time to prevent who she thinks was Xena (because her army was in the village) from killing her parents. While trying to protect her family from Xena's army, the adult Callisto accidentally kills her own father & mother.
 * This is actually done multiple times in the Doctor Who universe (as are most time travel theories).
 * In the series 4 episode, The Doctor doesn't want to avert , is convinced to avert it anyway, and then is forced to cause the disaster in order to avert a larger catastrophe.
 * Blink: "You're reading aloud from a transcript of a conversation you're still having?"
 * that already exists in is created by the Doctor's actions in "The Unquiet Dead".
 * And in series 5, the crack in the universe that's been causing so much trouble turns out to have been caused by . Fortunately, the crack transcends space and time so much that it extends back before the event which caused it, allowing the Doctor to  . That's once he's Tricked Out Time in a variety of ways in order to get himself out of  . Usually (well, seven times out of ten) he's a stickler about not interfering with your own time line, but desperate times call for desperate measures.
 * Inverted in Farscape. Sent back in time and desperate to keep things the way they were, the crew screws up, with each attempt to force what they know to be history resulting in the present time line getting worse. In the end, rather than the noncombatant survivors of the battle, they are . The memorial to peace becomes.
 * Crime Traveller had this as a central point, in theory. In practice, everything about the show's time travel suffered from galloping They Just Didn't Care.
 * The only time-travel arc on Babylon 5 involves this trope, and it is absolutely central to both the Myth Arc and the background mythology of the show. The Stable Time Loop is fully completed, so to speak, by the fact that
 * This concept became a major plot point in the fifth season of Lost (which Hurley couldn't quite grasp) though it was put to the test in the cliffhanger finale...
 * Particularly annoying with Sayid, which was not only implied to have already happened, Kate and Sawyer's interference in order to put things right seems to actually have caused  . Nice going, guys!
 * Quantum Leap was somewhat inconsistent on this trope. In episodes that directly impacted Al or Sam, they would have the entire memory of both things happening. For example:
 * Sam  tries to save his brother's life in Vietnam, which alters history and results in.
 * Actually.
 * In one episode, Congress is reviewing Project Quantum Leap's funding and leans on Al (acting as the project's representative) to have Sam alter history in ways beneficial to the US. Al tries to get Sam to prevent the U-2 spy plane incident, but Sam is in the past protecting a young attorney. At the end of the episode, the Congressman in charge of the committee is about to cut the project's funding when, in the past, Sam unintentionally corrects the attorney on a key piece of Constitutional law which she had wrong and she says could have made her fail the bar. Cut to the present, where the obstructionist Congressman is replaced by an older version of the attorney, who approves the project's funding for another year. It's never made explicit, but Al's surprise at the sudden change suggests that he's aware of the change.
 * However, in the episode about the Kennedy assassination, while Sam can't prevent from killing JFK, it then appears the reason he was sent back there was to prevent Jackie Kennedy from being killed, which most viewers would have assumed had already happened, whether Sam had anything to do with it or not.
 * In the Outer Limits episode "Tribunal", history professor and Holocaust scholar Aaron Zgierski is taken back to Auschwitz by time-traveler Nicholas Prentice (who turns out to be Zgierski's own great-grandson). While there, they rescue Aaron's "older" sister (who is only eight at the time) by bringing her into the future to live out her life free of Nazi oppression. History recorded Aaron's sister as dying at Auschwitz after being "dragged away" by a couple of guards, who were actually Zgierski and Prentice in disguise.
 * In the Outer Limits episode "Tribunal", history professor and Holocaust scholar Aaron Zgierski is taken back to Auschwitz by time-traveler Nicholas Prentice (who turns out to be Zgierski's own great-grandson). While there, they rescue Aaron's "older" sister (who is only eight at the time) by bringing her into the future to live out her life free of Nazi oppression. History recorded Aaron's sister as dying at Auschwitz after being "dragged away" by a couple of guards, who were actually Zgierski and Prentice in disguise.

Mythology and Religion

 * As mentioned, Greek and Germanic mythology tended to hammer on the idea (relying on prophecies instead of time travel) that You Cannot Change the Future. Even the Gods can't change the outcome of the story. (How many steps is Thor destined to take in the final battle of Ragnarok?) Not only that, but historians actually posit that Viking culture went into a prolonged funk over it, presaging the rise of Ingmar Bergman and Werner Herzog by centuries. (The lack of sunlight in wintertime didn't help.) Vikings in particular lamented the decline in pagan beliefs for exposing them to the horrors of existentialism, making them less resigned to the inevitability of death in battle. Meanwhile, the Greeks preferred to set up stories where characters would have Hubris enough to believe this trope did not apply to them, and then brutally swat them down in order to provide an entertaining Aesop. For examples, see You Can't Fight Fate and Self Fulfilling Prophecy.
 * The concept of Predestination. This concept is prevalent in all Calvinist churches (Reformed, Presbyterian, Baptist, congregational, Pentecostal) and in nutshell means that the life and final depository of a human being is pre-ordained and pre-determined by God and he or she can do nothing to avoid it. In other words, people are selected either to Heaven or Hell before they even were born.
 * This same concept is prevalent in Islam. The only way to avert the predestination is to get killed in Holy War, which earns you an automatic admission to Paradise.

Tabletop Games

 * In Palladium Books' Transdimensional Teenage Mutant Ninja Turtles, the GM was to have an important recurring character recognize the characters in a future era even if they hadn't met him yet in a past one.
 * In the time-traveller role-playing game Continuum, it's an ironclad article of Spanner faith that there is only one universe -- including one past and one future. A player will meet fellow spanners who've been affected by changes that are in the player's Yet, and you'd better do them or risk Frag.

Theme Parks
"By trying to change the past, I have actually caused it to happen!"
 * Featured in one of the videos leading into The Simpsons Ride at Universal. Professor Frink goes back in time to prevent Doc Brown's institute being bought by Krusty and converted into a theme park...only for his Delorean to hit the businessman who could have kept the institute open.

Video Games
"Kain: "Suppose you flip a coin enough times. Suppose one day... ""
 * Legacy of Kain uses this as an important plot point; more than one character has goals achievable only by finding ways to subvert this. Interestingly, while two entire games in the series take place in the past, while this trope is in effect, it still manages to have one of the most complicated sets of Gambit Roulette ever. One of the protagonists


 * Interestingly the first game in the series (Blood Omen) used a different kind of time travel - the kind where you go back, do something, and return to the present to find the effects of your actions having taken place. This was played straight with no mention of the paradox that would ensue from this kind of time travel. Two games later when time travel was reintroduced as a much more significant plot element, the rules were established around this instance of time travel, and it turns out Kain's original trip back to the past, as depicted in the first game without RetCons, already met the criteria for how someone can achieve a true alteration to the time line.
 * Final Fantasy VIII ending has this trope, with
 * Timesplitters Future Perfect is an example of this situation. Sergeant Cortez does, at least once per time period, meet a future version of himself that saves him, then when he reaches the period the future version is from, he then goes back to save his past self, fulfilling the time loop. EX: in the stage "What Lies Below", Cortez is saved by himself from the future, then has to defend his future self from zombies while the future self kills ghosts. Shortly afterward he wants to follow his future self, but his future self tells him "but where would you be if I hadn't shown up?". Future and Past Cortez part, then Past Cortez finds the ghost gun that Future Cortez found, steps into a wormhole, and ends back up where he was before, becoming Future Cortez. Now Future Cortez (who is controlled by the player) must kill ghosts while past Cortez shoots the zombies. When past Cortez asks to stay in a team, future Cortez tells him exactly what he heard from himself at this point. "Where would you be if I hadn't shown up?". The two part, and Cortez continues.
 * This does create an odd situation however in the "Scotland the Brave" stage, where Cortez finds a locked door, and his future self gives him a key, telling him to pass it on when he's done. When he reaches this point, he finds his past self, and he gives him the key, and tells him to pass it on when he's done, then leaves. The question remains however: where did the key come from in the first place if Cortez was passing it between time periods but never stopped to find it?
 * That's an easy one! The key has always existed. No matter how far back in time you go the key will always be passed down from future Cortez to past Cortez basically making the key The Constant or maybe a Time Abyss. Though, wait a second, wouldn't the key break down over time and deteriorate until it eventually snaps in the lock as Cortez uses it? Oh Crap...
 * After playing this trope straight for the entire game the final boss fight subverts it hard. Halfway through the fight Cortez realizes that he's outgunned and decides to go back in time and aid his past self to defeat the boss. This would be fine except that future Cortez never showed up to help you defeat the boss in the first place. The game never explains this Time Paradox and thus completely subverts the trope.
 * The game actually features two completely different forms of time travel, and it is implied that use of the first tore the universe a new one enabling the second.
 * In Prince of Persia: Warrior Within, The Prince travels to the Island of Time in hopes of preventing the Sands of Time, the source of all his misfortunes, from ever being created. He defeats the Empress of Time,  The second half of the game is about the Prince deciding to Screw Destiny and subvert this.
 * In Okami, the evil Orochi was defeated by a legendary hero named Nagi and a miraculous white wolf, who died in the attempt. The wolf was actually Amaterasu in physical guise, and was resurrected a century later as you, the player character. But then you travel back in time and discover -- you were the one who defeated Orochi then too, and the wolf who died was a different version of you.

Web Animation

 * A three-part episode of Red vs. Blue had Church travel back in time and try to change history to prevent both his 'death' and that of Tex, as well as attempting to stop the other difficulties that the Blue Team had to encounter at the time (such as the problem with Lopez's switch, and Tucker getting blasted by an RPG). He ends up accidentally causing, or failing to prevent, every major event of the series up to that point.

Web Comics
"Sarda: So now I know how she got there and what it feels like when I utterly screw with someone's lifelong ambitions."
 * All the Time Travel in Bob and George eventually resolves itself into this.
 * 8-Bit Theater has been explained by an in-comic character to be this, with the added You Can't Fight Fate.
 * At least, that's what the character believes. The character with enough nigh-omnipotent abilities to force things on the track he remembers.
 * Sarda did this to himself. As a young wizard, he time-traveled back to the beginning of the universe, only to find that a White Mage had gotten there first. After living through all of creation being formed around him, Sarda planned to put that White Mage into a pocket dimension before she could go back in time to the universe' start...only for that pocket dimension to be the beginning of the universe.

"Volair: "You can't change the future, Pierce. Past, future, it all fits together like a big, freaky jigsaw."
 * In Sluggy Freelance Bun-Bun's whole adventure in Timeless Space was based off this trope. As Uncle Time put it, "Life's so much funner with the paradox rules turned off."
 * In Homestuck, only Dave, the Knight of Time and Aradia, the Maid of Time get to go back in time and create Alternate Universes. Everyone else, no matter how much they've screwed around with the timeline, can only make Stable Time Loops, and the Trolls regularly insist that they've already lost the game and that You Can't Fight Fate. It probably helps that all in-universe timechanging items have built-in failsafes against causing paradoxes.
 * How Time Travel works in Umlaut House, as Volair explained to his future son here:

Pierce (Who just accidentally broke the UST between his future parents): "So the future you knows we're here?"

Volair: "No, but I will if you tell me the date you're from.""


 * A borderline example in Nodwick. Zorion visited the future and was upset to see there's only Dung Ages and a crater instead of his hometown now. How this could happen, indeed?
 * Time travel in The Way of the Metagamer runs entirely on predestination. This doesn't stop it from being ludicrously convoluted.
 * In The Adventures of Dr. McNinja, Chuck Goodrich is a time traveler from the future who comes to avoid The End of the World As We Know It play with this tropes. it's not like you can't change the past...you can change how it will be The End of the World As We Know It.
 * The Adventures of Dr. McNinja does use Branching Timelines, it's just that Cumberland Is The Center Of The Universe and everything in the universe is trying to kill us. A more accurate description of the various time traveling adventures of Chuck is that each disaster in itself acts to prevent all the other disasters that are waiting.
 * As explained by one character in a particularly nasty future, the branching timelines are the reason you can't technically change the past. See, since a future-you didn't come back in time to the present when you were taking The Long Path to the current future, you didn't do that, so if you go back in time, you create an alternate past where you did, and the versions of your friends and family in your current future-present will never see you again, and also their lives still suck.
 * In American Barbarian, Rick's attempt to go back results in his appearing as a character already seen.

Web Original

 * At the end of A Very Potter Sequel Hermione asks future!Draco what was really supposed to happen during their first year and Draco says that this was how it all played out originally, it just makes sense now that he lived through it.

Western Animation
"Professor: Choke on that, causality!"
 * Played straight on Futurama, where Fry ends up in 1947 and spends half the episode just trying to make sure his grandfather doesn't die. After the Professor warns him not to change the past unless he was already destined to change the past, Fry's extreme caution and stupidity result in his grandfather being vaporized by an atomic bomb. However, subsequent events make it clear that the man Fry killed was not actually Fry's grandfather, and that his real grandfather is . Of course, this is immediately followed by the Professor launching a full-blown assault on Area 51 with his intergalactic starship to retrieve the parts necessary to get home...


 * The standard rule for time travel in Gargoyles.
 * Goliath tried to convince Demona in the past not to turn evil, and she seems to take it all to heart. Unfortunately, one guy, even the love of your life, telling you to "stay good" is trumped by centuries of of being brutalized by humans. It's a true Tear Jerker to realize that Demona and Goliath were once really and truly Happily Married.
 * Xanatos uses this to his advantage. He gives two period coins to the Illuminati, along with a letter. The coins are like pennies in the past, but by the present they're very valuable and are the coins that started his fortune. The letter of course, is to tell him to do just that.
 * Later, Goliath attempts to use the time-travelling Phoenix Gate to save Griff from being killed during the Blitz in WWII London, after being accused of abandoning or murdering Griff by his companions. With incident after increasingly improbable incident occurring that indicates the universe has decided Griff is its new Chew Toy, Goliath ultimately concludes that fate will not allow Griff to get home and uses the Phoenix Gate to bring Griff back with him to the present, thus causing his original disappearance.
 * Mid-way through the Avalon arc, the Arch-Mage Took A Shitload Of Levels In Badass via a self-inflicted Stable Time Loop. Full details on that page.
 * Goliath winds up in a Bad Future (really All Just a Dream), and Elisa keeps egging Goliath on to use the Phoenix Gate to fix things. This is a hint that Elisa isn't what she seems, as by now, she should know how the Gate works.
 * Used on an episode of Justice League Unlimited. Brainiac 5 imports heroes from the past because history mentioned an incident where heroes traveled to the future. He tries to avoid mentioning how it turned out, of course, just to be sure things go the way they're supposed to, with only two of the three returning.
 * In the Darkwing Duck episode "Paraducks", Gosalyn warns Darkwing not to interfere into the past when they went back in time to his childhood. At first he doesn't and returns to the present, only to find that S.H.U.S.H. doesn't exist, the King, a two bit thug from Darkwing's childhood has taken over St. Canard and he serves as the King's cowardly lackey, never became Darkwing Duck. They go back and time and shut down the King for good and give little Drakey Mallard (Darkwing) the courage he needed.
 * The Fairly Odd Parents special "The Secret Origin of Denzel Crocker": Timmy and 21st-century Cosmo were the ones responsible for, which also indirectly led to his own birth due to
 * Somewhat subverted in the Invader Zim episode "Bad, Bad Rubber Piggy" had Zim send a robot rubber piggy into Dib's past at crucial points to kill him, only he survives by an inch each time (though everytime he comes close to death he's given robotic body parts from his father due to losing his own) and after many mishaps, he sends a piggy to the past to warn him not to send any piggies to the past in the first place. Unfortunately the premise of the piggies was they replaced something in the timeline they're sent to and one replaces Zim's brain at the end.
 * In Powerpuff Girls Mojo Jojo goes to the past to kill the adolescent Professor Utonium before he can create the Girls. The Girls pursue him. It turns out that in the past Professor was a lazy ass and a bully with no interest in becoming a scientist and creating the Girls, if it wasn't for Mojo's interference and the consequent encounter with and rescue by the Girls that gave him inspiration.
 * In the season 2 episode "It's About Time" of My Little Pony Friendship Is Magic, Twilight Sparkle is visited by her future self (from a week later, looking entirely worn) and told "whatever you do, don't..." with the sentence being cut off. Past Twilight then spends the whole week worrying about and trying to prevent whatever happens during the next week, with each incident causing her to gain the looks of Future Twilight, indicating she hasn't changed the future at all.
 * Played with in Beast Wars. While it is entirely possible to change the past and thus the future, thus finally answering Dinobot's soul searching about the nature of time travel and what that means for free will (if the past is immutable, than our ability to choose anything is a cosmic illusion). By changing the past, Dinobot learns that it is possible for an individual's choice to matter to the universe. Ironically however, with this new knowledge, it means that Megatron can change the past for the worst, and that the only choice Dinobot has is to invoke this trope.
 * Played with in Beast Wars. While it is entirely possible to change the past and thus the future, thus finally answering Dinobot's soul searching about the nature of time travel and what that means for free will (if the past is immutable, than our ability to choose anything is a cosmic illusion). By changing the past, Dinobot learns that it is possible for an individual's choice to matter to the universe. Ironically however, with this new knowledge, it means that Megatron can change the past for the worst, and that the only choice Dinobot has is to invoke this trope.