->''"You see Jake, there's rules to this stuff. Wishing an event to be changes elements before and after it; memories will be destroyed, babies will not be born, potential worlds could be evaporated by your wish."''
-->-- '''Prismo''', ''WesternAnimation/AdventureTime''

So you've decided to SetRightWhatOnceWentWrong. TemporalParadox is ''not'' a problem; once you make this change, the dark future (your old present? Whatever) will utterly change.

There's a very dark possibility of a SadisticChoice here. What if there's no such thing as InSpiteOfANail? What if the holocaust you're trying to prevent resulted in someone being born who will [[RetGone no longer exist]] if the situation of his parents getting together changes? What if there's [[ButterflyEffect millions of people who will be changed or erased against their will?]] What if this timeline had someone do a HeelFaceTurn who won't in the original timeline?

This is a heavy responsibility.

Many writers don't like dealing with this, so they'll often write that the better future is better ''in every way imaginable'' with no exceptions; and [[InSpiteOfANail nobody left out]]. Or that TheMultiverse means that world, those people and its choices somehow still exist... somewhere. But not everyone does, and it's a disturbing train of thought.

Related to ExpendableAlternateUniverse.
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!!Examples:

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[[folder: Anime and Manga ]]

* Kyon of ''[[SuzumiyaHaruhi The Melancholy Of Suzumiya Haruhi]]'' once changed the world back to his old one via TimeTravel. He still has nightmares of the implications of what he did, mostly because [[spoiler:it was a world where Yuki Nagato had her fondest wish: being human and quite possibly in love with Kyon.]].
* The second half of ''[[VisualNovel/SteinsGate Steins;Gate]]'' revolves around this. Realizing that the D-Mail experiments he's been conducting help cement a BadFuture [[spoiler:and guarantee the death of his childhood friend]], Okabe has to negate each one in order to avoid it. The problem? Most of those D-Mails altered the past in ways that granted his friends a good deal of happiness - including his own, as [[spoiler:the first D-mail prevented the death of the woman he's fallen in love with]].

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[[folder: Comic Books ]]

* In the "ComicBook/AgeOfApocalypse" arc of MarvelComics; set in a changed present where Charles Xavier was killed in the past; Magneto and Rogue have a son. The Time Traveler Bishop wants to change things back. Magneto supports Bishop in this, but reminds him that if they succeed; his son will be gone forever.
** Presumably this also bothered some writers; who later wrote that this world continued to exist as an AlternateUniverse. (Btw, Jean Grey stopped the nukes in the end.)
* TheDCU explored ''part'' of this with alternate timelines where good versions of Doomsday and Vandal Savage change things back; ironically back to where they are villains.
* The end of NeilGaiman's ''{{Marvel 1602}}'' sets right the circumstances that caused the temporal divergence that brought about the 'Age of Marvels' in the Elizabethan era. Thus, the timeline is overwritten, and history proceeds as necessary. The Watchers, however, step in and save the 1602 world as a pocket universe, kept in a glass globe by this version of Uatu.
* Pointed out in ''ComicBook/AstroCity''. Samaritan changes the future into a utopia, but his family was never born, and his old house is replaced with a future Taco Bell.
** It's revealed in "The Eagle and the Mountain" that this is actually one of Samaritan's powers. No matter what happens in history, he will still exist.
** One of the most famous issues, "The Nearness of You", has a different version, where a man is haunted by dreams of a woman he never met. [[spoiler:In a previous timeline, she was his wife, but following an off-panel CrisisCrossover, she was erased from existence, leaving only his memories of her.]]
* TheDCU's second {{Chronos}} spent some time trying to change history so his mother wouldn't die in a car accident. He eventually realised that the only way to ensure this was to [[RetGone never be born]]. He still exists as a time traveller, but his history up to the point he found Chronopolis has gone.
* In the {{JLA-Avengers}} story arc, at one point the histories of the DC and Marvel universes were altered by the retroactive effects of a history of the two universes interacting through their respective heroes. When they realized it needed to be fixed, they first asked to see what they were saving. Barry Allen and Superman saw their deaths, Hal Jordan saw that he would become the power-mad Parallax, Hank and Janet Pym saw [[NeverLiveItDown Hank striking Janet]], etc and they realized they were deciding the fates of potentially billions of people. The heroes decided to go forward in spite of what would happen to them.
* The cost of salvaging anything at all of the original multiverse in ''CrisisOnInfiniteEarths'' was to produce a new single universe and erase the original multiverse entirely from history. So, from a very real standpoint, ''[[PyrrhicVictory nobody]]'' [[PyrrhicVictory survived the original Crisis]] (except Superboy Prime and co., and maybe Power Girl and Psycho Pirate), and all the current heroes are temporal copies of the originals.
* The YoungAvengers team was started by the time-traveling villain Kang the Conqueror, who got a look at what he was going to grow into and ran away to our time to try and avoid growing into him. Which he did apparently succeed in, but unfortunately no Kang meant that none of the many fights he'd had with ComicBook/TheAvengers over the years and in some way that lead to almost all of them being killed, the small amount of the alternate world we see looking pretty dystopian, and the members of his team who were children of Avengers members (except for the daughter of the one whose death might actually have been ''prevented'' in the new timeline) fading out of existence. He realized that [[ButNowIMustGo he had to go.]] Although we've found out since that he's still time-traveling trying to find a way to avoid becoming a villain, he's just looking for a way that won't wreck things for everyone.

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[[folder: Fan Fiction ]]

* Averted in TheThreeWhooves, where [[spoiler:Three's memory is erased to make sure his experiences don't change his actions]].
* A ''Manga/FullmetalAlchemist'' SlashFic called [[http://www.fanfiction.net/s/9035781/1/Redo "Redo"]] explores this problem. Ed and Al, living TwentyMinutesInTheFuture from the end of the manga/''Brotherhood'', are sent back in time by a rogue alchemist to right before they traveled to Lior. They struggle with how they're now given the opportunity to save some people who died and situations they screwed up the first time, but also need to make sure everything that went ''right'' before does as well.

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[[folder: Film ]]

* Subverted in ''Film/StargateContinuum'' when the government in the new timeline refuse to help the team try to SetRightWhatOnceWentWrong.
-->'''Major General Hank Landry''': ''My goodness, people, the arrogance of what you're asking us to help you do is mind-boggling!''
** And played relatively straight anyway once everything starts going to pot (Baal dies, snakeheads attack, Earth in deep trouble). Apparently, ''Earth'' humans (as opposed to "alien" humans) living as slaves under the Goa'uld is not to be thought of - and we'd be better off never existing in the first place.
** To be fair, the team from the original timeline always wanted to fix everything, they just never had a chance before then.
* The ending of ''TheButterflyEffect'' invokes this trope: [[spoiler: The main character goes back to the beginning, and ends his lifelong friendship/love (depending on the timeline in question) with the female lead before it starts. It works.]]

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[[folder: Literature ]]

* [[AvertedTrope Averted]] in ''Literature/{{Animorphs}} Megamorphs 3''. Some things in the altered future may have been better, many things were worse, but in the end when Rachel asked Cassie if they fixed everything, all Cassie could say was that "they put it all back."
** Although, seeing how the [[AlienInvasion Yeerks were just a couple steps from taking over the Earth]], [[ThoseWackyNazis the Nazis won World War II]], "unfit" people were being eradicated, rebellious people were being "reeducated", "fit" people were forced to breed repeatedly, and [[ArsonMurderAndJaywalking the only videogame in existence was Pong]], I doubt it could be much worse.
*** Yes, originally, that was true. But once the Ellimist and Crayak sent the kids back and they started trying to stop the BadFuture from happening, other, possibly good things started happening. D-day still occurred, for example, but Hitler was just a driver, and there was the distinct possibility that the Germans were the good guys. It was never made clear (which was completely intentional, of course).
** In ''Megamorphs 2'', this trope is in effect big time, though played...interestingly. To elaborate, the Animorphs go back to the end of the Cretaceous Era and soon discover not one but two sentient alien races who had colonized the Earth. They also soon discover that there is a giant freakin' comet flying through the sky, which [[TheSmartGuy Ax]] informs the group will just barely miss the Earth, based on its trajectory. The two alien races are at war with each other, but with the Animorphs' help, the "good" aliens drive off the "bad" ones. The "bad" ones respond by moving the comet off its path, aiming it towards the Earth in order to wipe out the entire "good" alien population. If you know anything about the age of the dinosaurs, you've probably guessed by now where this is going. The "good" aliens try a last ditch effort to blow the comet back into not hitting the planet and killing them all, but Tobias secretly has Ax rig the explosive to be a dud. Tobias insists that [[IDidWhatIHadToDo he did what had to be done]], realizing that in order for humanity to rise, the Animorphs can't change history such that the "good" aliens (and the dinosaurs) survive, because they know from the lack of either in the present that they don't. Tobias also insists that he didn't consult the others because he didn't want them to live with the guilt of having condemned an entire sentient species to extinction. This still leaves Ax and Tobias with that guilt, and the question of whether dooming one innocent species to ensure their own existence was the right choice. This therefore is the unusual case of ensuring a StableTimeLoop being highly morally questionable.
* Addressed in Creator/OrsonScottCard's novel ''Literature/PastwatchTheRedemptionOfChristopherColumbus'', where the organization that just discovered time travel is quite aware that interfering with the past will erase the existence of everyone in the current timeline and insists on having the world vote on whether or not to SetRightWhatOnceWentWrong. As humanity is facing imminent extinction anyway at that point, the vote passes.
** It should be noted that, at first, they ask scientists to make sure that there's only one reality. This takes years, but eventually scientists confirm that time travel will not result in a separate timeline but will rewrite reality. How they can possibly confirm this is anybody's guess.
* In the Creator/PeterDavid Franchise/StarTrekExpandedUniverse novel ''Imzadi'', Admiral Riker wants to go back some thirty years to the time of late-season [[Series/StarTrekTheNextGeneration TNG]] to save Deanna's life, since he believes someone already altered time by traveling back to kill her; Data objects on these grounds. When it's done and everybody has time-traveled home, the Guardian of Forever--time-travel mechanism of choice today--points out that "All is as it was." When asked why it didn't bother to mention that yes, Riker was restoring the proper flow of history, it answers [[spoiler:YouDidntAsk]].
* In ''The Time Ships'', the Time Traveller's second trip into the future sends him to a completely different world from the one he remembers. He concludes that with every use of the time machine he is potentially committing murder on an unimaginable scale and vows to prevent himself from ever creating the machine. Later subverted when it turns out that the many worlds model is in effect.
* Discussed and averted in ''Literature/IslandInTheSeaOfTime'' and ''Literature/SixteenThirtyTwo'', both novels involving the permanent transplantation of a modern town to the past. They came to the conclusion that it was a once-in-a-universe cosmic event, so they were astronomically unlikely to go back, therefore they didn't have to worry about changing the future because they'd already changed it by their very presence.
* [[spoiler:Edeard]] encounters this in the Literature/VoidTrilogy.
* ''Literature/TheRifter'': Faced head-on. John, by going to Basawar at an earlier point than the point where he got the key to the gates from Kyle, changes history (and creates an alternate version of Kyle who never traveled to Nayeshi and lost the key); on the whole, the new history is for the better (thanks to American liberalism, the power of love, and perhaps the providence of Parfir), but bad things happen too -- for example, John destroys northern Basawar and all its living things, which wouldn’t have happened in the original time.
* Handily averted in John Birmingham's ''Literature/AxisOfTime'' trilogy, where a multinational fleet from the 21st century ends up in the middle of WorldWarTwo with no way to get back. The question is moot, as the appearance of the fleet results in a battle between them and the American task force heading for Midway. By the time the main characters figure out what happened, history has already been affected in a major way. Also, according to the novel, the characters know they're not really in their own past but in an alternate reality, so any changes they make will not affect their own timeline. For bonus points, Einstein himself confirms this.

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[[folder: Live Action TV ]]

* Played straight in ''Series/StarTrekVoyager'' "Timeless", in which Harry Kim is driven to SetRightWhatOnceWentWrong, a mistake on his part which killed the crew except for him and Chakotay who were in the Delta Flyer, but both Chakotay and his girlfriend know that this will cause them never to meet. Starfleet also saw it as dangerous and sent [=LaForge=] to stop them.
** Voyager also had a story arc ("Year of Hell", parts 1 and 2) about an an alien WellIntentionedExtremist who built a weapon that could erase things from history; his intent was to get rid of his species' enemies, but in so doing managed to get his wife killed, leaving him continuously trying to undo the damage by erasing more civilizations. Ironically, even after hundreds of years doing this he never realized what he really needed to erase was [[spoiler:the weapon itself. Once Voyager's attack causes it to malfunction and erase itself from history, everything he ever changed returns to normal]].
*** It's not that he didn't realize it, it's that he wouldn't consider that a solution. The entire point of the weapon was to wipe our his civilization's enemies. If he has his wife back but that core goal isn't satisfied, then he's still failed.
** [[MyFutureSelfAndMe Admiral Janeway's]] plan in the finale is to send Voyager home NOW. Captain Janeway points out that she did get Voyager home after another sixteen years. The plot takes over before they get too philosophical, to the disappointment of many watching.
** In another ''Voyager'' episode, a NegativeSpaceWedgie splits the ship into various time periods, though which only Chakotay may pass. At the end, Janeway from just before the mission offers to have the ship be restored to ''her'' time, thus preventing the ship from being trapped in the Delta Quadrant. Chakotay refuses, claiming that they have helped far too many people in the Delta Quadrant to erase this. He conveniently neglects to mentions that his own ship would still be trapped in the Delta Quadrant if they follow Past!Janeway's plan.
*** The same thing is proposed by a Past!Romulan commander who ends up communicating with Present!''Voyager'' through a NegativeSpaceWedgie. He offers to warn Starfleet of ''Voyager''[='s=] fate just before the launch, but Janeway refuses. It would have been moot anyway, as Tuvok reveals later that, according to historical data, the commander died long before the ''Voyager'' was launched.
* Mentioned and averted by way of Q in ''Series/StarTrekTheNextGeneration''. Picard's artificial heart is damaged and he's about to die, so Q gives him the opportunity to change his past to prevent the injury that led to him getting the transplant. Picard worries that any action he'll take in the past could have disastrous consequences, but Q brushes him off with, "Nothing you do will cause the Federation to collapse or galaxies to explode. The only life at stake here is yours. In short, you're not that important."
** Of course, while it doesn't have disastrous consequences for anyone else, the consequences to Picard's own life after not getting in the fight that caused the injury are so bad he immediately asks Q to change it back even if he does die. So averted on a galaxy-wide scale, but definitely present in his own life.
* On {{Lost}}, several have tried to save the past...and ''all'' fail miserably and ''cause'' the event, since everything that has or will happen has already happened. Most notably, Daniel's attempts to [[spoiler:reset time so that 815 never crashed by stopping the Incident]] not only results in [[spoiler:his death]], but probably ''caused'' the Incident, since [[spoiler:we see Pierre lose his arm]], a event referenced in the very first episode with him in it.
** Maybe. ''Something'' was going wrong at the Swan site before they stepped in.
** And it seems as though he both succeeded and failed. [[spoiler: The heroes have destroyed the island in the past but seem to have been returned to the present in a timeline where they didn't (ie, their original timeline). In the timeline they did affect, there are versions of them running around that never crashed on the island. Its unclear right now whether or not these are completely separate universes or all these characters are now somehow on the same Earth.]]
*** Neither. [[spoiler:It's some sort of ghost world. They're all dead.]]
*** More specifically, [[spoiler:it's a dimension outside of linear time which they created by using power from a nuclear bomb and the island itself. The math involved fits neatly on a single page of Daniel Faraday's notebook.]]
* Acknowledged and arguably justified in an episode of ''Series/{{Buffy|the Vampire Slayer}}'', involving not time travel but alternate realities. In the Season Three episode "The Wish", Cordelia wishes that Buffy had never come to Sunnydale, creating an alternate reality in which the town is overrun by vampires. Alt-Giles figures out how to reverse the effect, but at the last second, the demon responsible for it tries to stop him, asking why he thinks the alternate (original) universe is any better than the one he knows. Giles' response? "Because it has to be."
* Done beautifully in the Series/DoctorWho episode ''The Fires of Pompeii.'' The Doctor is saddled with the choice of not setting off Vesuvius, thereby saving Pompeii, or sending those people to their deaths in order to keep history intact [[spoiler:and to keep the Pyroviles from conquering Earth. Finally, with support from Donna, he sets off the volcano.]]
** Comes up again later in "The Waters of Mars;" only this time, [[spoiler:The Doctor changes history by choosing to intervene.]]
** Turns up even earlier in ''[[Recap/DoctorWhoS12E4GenesisOfTheDaleks Genesis of the Daleks]]''. The Doctor is given an opportunity (an order, even) to prevent or seriously alter the creation of the Daleks. The only obvious downside is that at that point the Daleks hadn't done anything wrong (yet), and so he'd be committing genocide against a thus-far innocent race, who he knew would turn evil and try to wipe out entire species... [[spoiler: he didn't, merely delaying their development for a while, for which [[TimeyWimeyBall causality]] is thankful]]
** And according to {{fanon}}, enabling Davros to survive when his creations turned on him. When he was revived later in the original series, he eventually plunged the Daleks into civil war and undercut their threat to the universe for some time.
** The scandal surrounding Jimmy Savile turns ''[[Recap/DoctorWho1985JFIGSAFixWithSontarans A Fix with Sontarans]]'' into this for the Doctor and Tegan.
* An episode of ''Series/StarTrekDeepSpaceNine'' has the Defiant crash on a world populated by the crew's descendants (and a future Odo), thanks to a time loop. The characters decide they have no choice but to make sure these people live, and prepare to trap themselves in the past. [[spoiler: Unfortunately, future Odo couldn't stand to let Kira die again, so he screws with the ship, allowing it to escape and erase the entire colony.]] Kira doesn't take it well.
* ''Series/StargateSG1'' does it in the episode "2010" with Carter's husband wondering if the other timeline will really be better and what happens to them if the plan succeeds. Carter then bluntly tells him that "they" won't exist or exist but in a different way and that the new timeline cannot be worse than the absolutely certain destruction of humanity in less than 200 years. As we know, despite the new enemies appearing later on, she was entirely right.
* Happens two times in ''TheXFiles'': played straight in "Synchrony" in which a researcher travels from the future to destroy his own research because of the chaos created by practical time travel in his future. Subverted in "Triangle" in which Mulder, as the time traveler, attempts to prevent Nazi agents from stealing "Thor's Hammer," a supposed superweapon aboard a cruise ship. [[spoiler:It was AllJustADream...or was it?]]
* In the ''Series/{{Supernatural}}'' episode "The Song Remains the Same", the angel Anna goes back in time to kill John and Mary Winchester before Sam and Dean are born in order to prevent Sam and Dean from kickstarting the Apocalypse. Sam and Dean follow her to save John and Mary but take the opportunity to try to convince Mary to remain childless, as Sam and Dean are willing to cease to exist to stop the Apocalypse. This plan fails because the angel Michael, who is pro-Apocalypse, stops Anna and erases John and Mary's memories of the event.

[[/folder]]

[[folder: Video Games ]]

* While it's hard to tell (since the game is currently in alpha), the plot of ''{{Achron}}'' will probably explore this. It's already been referenced on the developer blog before.
* It's implied in a letter from Lucca in ''VideoGame/ChronoCross'' that the main characters of ''VideoGame/ChronoTrigger'' have to die as karmic punishment for changing the future. This trope is the springboard for the entire plot of ''VideoGame/CrimsonEchoes''.
* Aversion: Not TimeTravel, but worth commenting on; an AssPull justification that Marche of ''FinalFantasyTacticsAdvance'' gives regarding changing Ivalice back into [[UpTheRealRabbitHole "The Real World"]] is that surely the MagicalLand Ivalice will continue to exist as AnotherDimension after he destroys it.
* ''VideoGame/PokemonMysteryDungeonExplorers of Time/Darkness/Sky'' reveals in its final chapter that [[spoiler: because you, Grovyle, and Dusknoir all came from the future, the three of you will be erased from the timeline if the Time Gears are returned. The player character gets better.]]
** One of the bonus chapters in ''Sky'' reveals that even though the BadFuture was prevented, it still exists in some other universe. [[spoiler: It gets fixed in this universe too]], but thinking about this further can lead to the conclusion that it might still be sticking around in ''other'' universes.
* In Telltale's ''VideoGame/BackToTheFuture'', First Citizen Brown (an alternate version of Doc) pulls this on Marty when he discovers that, in Marty's timeline, [[spoiler:Brown's wife Edna is a lonely batty mess]]. It turns out that Marty inadvertently fixes things anyway, as [[spoiler:Marty inadvertently fixes up Edna with Kid Tannen, and they end up being moderating influences on each other.]]
* Discussed and Averted in ''VisualNovel/VirtuesLastReward. [[spoiler:Although the goal of the AB project is to prevent the release of the Radical-6 virus, the timelines in which Sigma and Phi failed to do so still exist. Phi talks to you about it briefly as part of the Multi-World Interpretation, and Tenmyouji and Quark talk about it during the Golden Ending, and some ethical implications thereof.]]

[[/folder]]

[[folder: Webcomics ]]

* ''GeneralProtectionFault'' had a massive story arc in which the future son of the two main characters went back in time to prevent his BadFuture from occurring, knowing full well (and accepting) the fact that doing so was likely wipe him from existence. [[spoiler:It didn't. Probably. That arc was running on weapons-grade MindScrew towards the end.]]
* Briefly addressed in ''Webcomic/SchlockMercenary''. The cast didn't dwell on it much, probably because their universe was doomed anyway.
** Though [[http://www.schlockmercenary.com/d/20050410.html the metaphor used]] when he makes the jump softens the blow. It also helps that it had only been a few weeks.

[[/folder]]

[[folder: Western Animation ]]
* In the 5th season premiere of ''WesternAnimation/AdventureTime'', Jake is faced with something resembling this dilemma. While this example deals with an alternate timeline created by [[spoiler: Finn's wish for the [[BigBad Lich]] to have never existed]] rather than genuine time travel, Jake is informed by [[spoiler: Primso]] that:
--> "...(T)here's rules to this stuff. Wishing an event to be changes elements before and after it; memories will be destroyed, babies will not be born, potential worlds could be evaporated by your wish."
* Averted in the ''JusticeLeague'' episode "The Savage Time", where Alternate Batman doesn't like living in an authoritarian regime after the Allies lost WorldWarTwo.
-->'''Martian Manhunter''': ''You understand that if we do change the past, you - this version of you - will never have existed?''
-->'''Alternate Batman''': ''Nothing would make me happier.''
** Also, when Alternate Batman mentions his parents were killed for opposing the government, he later seems hopeful that they'll have survived if the Justice League changes the past. Superman mentions very tactfully that this may not be the case ([[DeathByOriginStory they don't]]).
* ''WesternAnimation/StarTrekTheAnimatedSeries'' episode "Yesteryear". We certainly hope Thelen the Andorian got a comparably good job in the rewritten timeline. At least he accepts his fate bravely and Spock wished him a long and prosperous life in whatever circumstances he would be placed in. (Like most Trek time travel, it's unclear whether or not he got to stick around in a [[ALternateHistory divergent timeline.]])

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