Chrovos: And utterly shattered time in the process.
Donut: [upset] Ugh! They did it! They saved him!
Time Travel is complicated business. With nearly infinite moments spanning both forward and backward in time, all interacting with one another, it would be impossible for someone to know exactly what changes will have what consequences. But that won't stop you from playing to play the odds. You have a Time Machine and you're going to use it, damn it! Time to kill Hitler, save JFK, and stop the Black Plague with modern medicine! What could possibly go wrong?
You get back, however, only to find disaster. Turns out, Hitler was holding the Reich back, JFK's death brought the nation together, and the plague kept Europe from disastrous overpopulation. If that wasn't bad enough, now there's an infestation of Clock Roaches devouring everything in their way as they hunt down whoever threw things out of whack, and the universe is now falling apart at its seams.
This results in two available options: learn to live with this new reality, or stop the inciting incident of all of this: you. To fix every problem you caused, you'll have to undo every change to history you made during your time travels and make sure events play out as they originally did. That means you'll have to let young Hitler live on to lead his merry band of Nazis (what else did you expect was going to happen when you go back in time to kill Hitler?), allow JFK to become an American martyr, and sabotage any potentially successful attempts to neutralize the Black Plague.
However, some Fridge Logic reveals that atoning time travellers aren't technically limited to those two options. If the technology for time travel allows one to make another attempt at changing history for the better, and if messing with history doesn't bring about worse consequences such as Upsetting the Balance or an infestation of Clock Roaches, one can simply set out to find and iron out all the small details that could set the bad future in motion, thus achieving the desired result while minimizing or even nullifying any damage. Don't expect it to be ever attempted or addressed, though. Writers would rather play this trope straight for the same reason they prefer forcing a pregant character to choose between aborting her baby or raising it over having her give it up for adoption: because it's bad for drama.
This takes place when either because of a Bad Future or Temporal Paradox, the hero (or the villain, or the Time Police) has to undo a previous attempt to fix history. The fixer and the breaker don't have to be the same person, but they usually are. Expect The Time Traveller's Dilemma to be brought up or for the heroes to perform a Reset Button Suicide Mission.
A Sub-Trope of Nice Job Breaking It, Hero! and sister trope of Make Wrong What Once Went Right and Set Right What Once Went Wrong. Often leads to The Story That Never Was. See also Reed Richards Is Useless, which this trope generally hinges on.
Contrast You Already Changed the Past.
As these are usually the resolution to a plot, all spoilers are unmarked.
- In Flashpoint, Barry Allen goes back in time to stop his mother's murder, but the resulting ripple effects create a future where the Earth is devastated, Superman is a lab rat of the U.S. Military, Atlantis and Themyscira are going to war with each other, and Bruce Wayne is dead, with his parents as Batman and the Joker respectively. He eventually has to stop himself from his own attempt, which ends up rebooting the DC Universe into The New 52.
- Booster Gold
- One storyline had a future Blue Beetle offer to Booster the chance to go back into the past and save his friend, Ted Kord, before Maxwell Lord could kill him. Booster accepts despite Rip Hunter's warning that the past can't be changed due to being "solidified time" and he, along with the Dan Garret and Jamie Reyes Blue Beetles, go back and save Ted and even defeat Maxwell. However going into the present they find out Maxwell initiated his plan earlier then expected with the OMACs and took over the world. What's more, the future Blue Beetle is actually the Black Beetle and is part of a group of time-traveling supervillains dubbed "The Time Stealers". Booster, Ted, Dan and Jamie team with the surviving Justice League members to fight Maxwell and barely win the day... only for the Time Stealers to show up and are now poised to take over themselves. Ultimately, Ted realizes the only way they can win is to go back in time and allow history to play out, giving a heartful goodbye to Booster as he uses a time machine and returns to the day of his death.
- Another story, The Gift, had Booster want to give Bruce a wedding gift for his, then, upcoming wedding to Selina (aka Catwoman). Inspired by the event of "For The Man Who Has Everything", he goes back to the day Bruce's parents were killed and prevents their murder. The changes are a mixed bag: Thomas and Martha are still alive sure, but Penguin is the president, Ra Al Ghul has two nations under his reign, there's a rampant Joker virus that causes people to kill themselves (as we see with Hal Jordan at the start), Dick Grayson is the Batman in this version who uses guns and Catwoman is an psychopathic murderer who only meows and is in no way acquainted with Bruce. After some poorly thought out shenanigans by Booster (to the point Skeets is temporarily destroyed and he's stuck in the timeline for a year) that result in the death of this timeline's Waynes, Alfred, Catwoman, and Batman. Booster tricks Bruce into going back to the day the Waynes initially died and allow events to play out (albeit the alt-Bruce killing himself after seeing this) to fix the timeline.
- In the Andromeda fic For Just a Day, Dylan travels back in time and prevents the Fall of the Commonwealth by warning it of the Nietzschean uprising. Then it turns out this was part of the villain's plan to shatter civilization completely - there will be a second uprising, this time with Nova Bombs.
- In the Invader Zim fic Blessing in Disguise, Red and Purple go back in time to kill Zim as he's born, thus preventing any of his screw-ups from damaging the Empire. Unfortunately for them, this leads to them not being Tallest, and Irk being in a losing war with Meekrob. They then have to go back in time again to stop themselves from changing history.
- In Justice League: The Flashpoint Paradox, Barry Allen goes back in time to save his mother from being murdered, only for it to result in a world on the brink of collapse as the Amazons and Atlanteans go to war, Superman is a U.S. government lab rat, and Metropolis is in ruins. He has to stop himself from doing it in the first place in order to restore his own reality, albeit with noticeable differences like gaining his New 52 costume.
- About Time: Tim goes back in time to stop his sister from becoming an alcoholic that would eventually lead to a major car accident on his daughter's first birthday. In doing so, his daughter is never born, so he goes back in time and stops himself from stopping his sister.
- Pretty much the entire plot of the 2004 film The Butterfly Effect, where Evan the main character finds he can travel back in time to inhabit his former self during those periods of blackout, with his adult mind inhabiting his younger body. He attempts to change his terrible present by changing his past behaviors and set things right for himself and his friends, but there are unintended consequences for all that end up making things much worse for Evan throughout the film. The director's cut ending shows Evan deciding that the only way to undo all the damage he's done is to make sure he was never born, traveling back in time and strangling himself with his own umbilical cord. In the theatrical version, he just wards off the girl he knew since childhood while they're still young. Making sure they never met and preventing pretty much everything in the movie from coming to pass.
- In 11/22/63, Jake saves JFK. This is a mistake in and of itself, as this causes the Earth to have major earthquakes, which causes fanaticism and war to skyrocket. But it also leads to the election of George Wallace, who bombs Hanoi in an attempt to end The Vietnam War, which results in a huge number of subsequent nuclear incidents and environmental collapse. Eventually, Jake admits his mistake and goes back to let JFK die.
- The End of Eternity is about an organization that constantly reshapes human history and makes it better. The ending reveals that there is another organization from the far future which foresaw the Eternity's "improvement" policy will ultimately lead to humanity stagnating and dying out, so they retcon it out of history.
- Played for laughs in the short story "Wikihistory" by Desmond Warzel. Adolf Hitler, the Third Reich, and World War II are crucial to the formation of the International Association of Time Travelers, but newbie IATT members who didn't properly read the rulebook keep going back in time to kill Hitler. Each time, veteran member SilverFox316 goes back and stops the newbies because no one else will do it, and his posts on the message board get more frustrated with every trip.
- In the beginning of The Company of the Dead a time traveller on board the Titanic hands the lookout a pair of night vision binoculars and so the ship avoids the fateful iceberg - the problem is that time soon rights itself and the ship hits a different iceberg a few hours later, sinking the ship with an even more catastrophic loss of life due to being far out of the range of both the Carpathia and Californian - however there is one key difference: John Jacob Astor survives the sinking, setting off a chain of events where the USA never enters the First World War and, as a result, the east coast is occupied by Greater Germany and the west coast by Imperial Japan.
- Alex Scarrow's Time Riders novels have it as a set in stone rule for our heroes; no matter what, history can only go one way. It's poorly elaborated why, but that's just how it goes. It turns out it's mainly to avert this trope - because a single change can have incredible unforeseen consequences downtime, even a simple act of goodwill could result in a far worse future than you could ever have hoped for. A good example of this trope actually happens by accident in the sixth book, City of Shadows. An assassin follows the gang into Victorian London, but arrives early because of a mishap, and accidentally catches Jack the Ripper before his final kill. Sounds good, right? Well, not really - Jack the Ripper turns out to be a prominent noble, and his murder-in-self-defence is pinned on his would-be victim, a poor working-class woman whose hanging makes her a martyr figure for a socialist uprising in Britain. The royal family flee to Canada for safety, and one by one the twentieth century sees socialism rise in most of Western Europe (except France, for some reason). By the time of 2001, Socialist Britain is oddly old-fashioned, implied to be a police state, and on the verge of nuclear war as the US wants to send nuke parts to France in a reversal of the Cuban Missile Crisis, and it's implied that a nuclear holocaust follows soon after. As such, our heroes have to make the agonising decision to allow an innocent woman to be horribly murdered and to let her killer get away.
- A short story by Stephen Fry has a man travel back in time to have Hitlers father drink water that renders him infertile. But the new present is ruled over by Pragmatic Villainy Nazis, who simply fed the Jews the water during the Holocaust. So he goes back again and puts rats in the water, so it has to be replaced.
- Season 2 of The Flash (2014) ends with Barry traveling back in time and preventing his mother's death, resulting in a brand new timeline. However, after Wally ending up in critical condition and losing memories every time he uses his speed, Barry is forced to ask Thawne to go back in time and kill his mother all over again.
- Mystery Science Theater 3000: In Time Chasers, Crow travels back to the 80s to steer a younger Mike Nelson away from the string of low-paying temp jobs which would eventually get him trapped in space watching bad movies. He succeeds by convincing Mike to focus on his rock band instead. But upon returning to the present, Crow finds that Mike's place on the Satellite of Love is now occupied by Eddie, Mike's hard-drinking Jerkass brother—while Mike's music career ended with early death in the middle of a show, just as his band was on the verge of stardom. Crow fixes everything by traveling back to the 80s again and talking his own past self out of trying to change the past.
- The Red Dwarf episode "Tikka To Ride" had this as its premise; the crew of the Starbug inadvertently prevent JFK's assassination, only to find that in doing so they turned Kennedy from a martyr to a disgraced convict; in the altered timeline, President Kennedy was impeached in 1964 for sharing a mistress with a Mafia boss, and sentenced to three years in prison. J. Edgar Hoover became president and was blackmailed by the mob, who made him allow the USSR to install a nuclear base in Cuba in return for Mafia cocaine trafficking between Cuba and the States. As a result, all major US cities were evacuated. The crew then travel to 1966 and have the now-disgraced Kennedy travel back with them to 1963 so he can shoot his past self, saving the US and his image in the process. He thanks the Starbug crew for redeeming him and then fades away.
Lister: It'll drive the conspiracy nuts crazy, but they'll never figure it out.
- A major theme in Doctor Who where changing a moment in history, even for good reasons, could lead to The End of the World as We Know It:
- "Father's Day" shows Rose Tyler traveling back to see father die in a hit-and-run accident, but ends up saving him. This causes a Time Crash that creates flying dragon demon things trying to unmake reality and the TARDIS got erased too. These events are (mostly) undone after Rose's dad dies, which he did as a Heroic Sacrifice in order to get things back to normal.
- In Classic series, although this didn't happen, it was already mentioned twice that changing history for good could be a bad idea: first in "The Aztecs" when First Doctor's companion Barbara was disguised as a goddess and her decision of forbidding Human Sacrifice would wipe out this civilization; and later in "Earthshock" when Fifth Doctor was unable to save his companion Adric, which would mean the end of humanity by the bomb made by the Cybermen would crash on the present Earth (instead went to prehistoric Earth and destroyed the dinosaurs instead of a meteorite... with Adric inside).
- Quantum Leap: The show's premise was the inverse, that Sam was travelling through time setting right what had once gone wrong, but this trope (or something pretty close to it) was namechecked in an episode, "The Boogieman", where Sam had an encounter with the devil, who takes on the guise of Al and complains malevolently that Sam has been undoing his work of setting wrong what once went right... Except that It Was All A Dream in the end, or mostly, or something. Don't think too hard about it, he'll be somewhen else next week.
- Star Trek: The Next Generation:
- One episode opens with Picard apparently lethally injured by a stray energy blast which happens to have destroyed his artificial heart. As he walks into the light, Q appears and (after claiming to be God and taunting him about how a natural heart would have survived the incident) offers him a chance to go back to his wild college days and avoid the bar fight and subsequent near-lethal stabbing that resulted in needing the artificial heart in the first place. The resulting timeline ended up essentially the same (Q promised to avert any Butterfly Effect or For Want of a Nail as part of the deal) but the changes to his actions and attitudes then carried forward, resulting in Picard himself ending up a boring, timid man who only ever played it safe and never learned how important it was to seize the moment and make his life count. It takes only a few hours in that dull life before Picard is calling on Q to let him undo the change, even if it means dying in the original timeline. Turns out the doctors in the present are able to save him after all, and he's left musing whether Q was even there or if it was All Just a Dream.
- Star Trek: Voyager:
- The entire plot of the two-parter "Year of Hell". The antagonist built a machine that can selectively delete targets from the timeline in order to change history and make his people strong. He succeeded, but at the cost of the lives of his family. Since then he has spent years studying time patterns in an attempt to fix this. In the end, this happens by accident. It is only achieved by erasing the object that made the changes possible: the time-changing machine, thereby undoing everything it has wrought.
- In one episode of Teen Angel, Marty manages to travel back in time and convince his past self to not eat the bad burger that killed him, but other people die instead, no matter how many times Marty goes back, because of the burger (either because they are the ones who are it or, in one case, Marty tossed the burger out the window and it fell on their head, blinded them, and made them get run over by a car). With the entire cast now in Heaven, Marty accepts that all he can do is go back in time and allow his past self to die to save everybody.
- "Profiles in Silver," a The Twilight Zone (1985) episode, depicts a time-traveling historian inadvertently saving his Famous Ancestor, John F. Kennedy, from Lee Harvey Oswald's assassination attempt — only to learn that Kennedy's survival will precipitate World War III. Sooner than send Kennedy back to certain death, the historian replaces him and is killed in his place. The end of the episode shows Kennedy in the future, teaching a history class.
- Life Is Strange
- Max finds out in the middle of the story she has the power to travel back in time via any old photos she uses her powers on. So she attempts to go back to when she was younger and prevent Chloe's father from going on a trip that resulted in his death. When she goes back to the present however, she finds out that Chloe is paralyzed from the neck down since her father brought her a car for her 16th birthday and she got into an accident. The lifestyle is so hard on Chloe and her parents' finances that she ultimately ask Max to kill her (which is up to you). Either way, Max goes back in time to correct history.
- This is ultimately the result of the "Save Arcadia Bay" ending. Since Max first started using her powers this caused a temporal anomaly to form as a typhoon that'll destroy the town. The only way to prevent it is for Max to use a picture she took when she first discovered her powers and use it to go back to the day and allow Chloe to be killed by Nathan Prescott which Max had prevented and set the events of the game in motion.
- Red vs. Blue: After creating a Temporal Paradox the season prior trying to save Washington from getting shot, Season 17: "The Singularity" deals with the Reds and Blues trying to undo various other paradoxes caused by Chrovos and Genkins, who are trying to break time in order to free the former from their Extranormal Prison. The season ends with the Reds and Blues undoing the original paradox, allowing Washington to get shot and become brain-damaged.
- Ben 10: Alien Force: In the episode Time Heals, Gwen uses a time travel spell to prevent Kevin's mutation. Because of this, Kevin is too weak to defeat Hex, resulting in him taking over the world as well as: Kevin being turned into a stone monster and enslaved by Charmcaster, Ben being imprisoned, and Gwen dying. With the help of the alternate Ben, Gwen uses the spell again to erase her past self's memory, allowing the timeline to continue as it should.
- Family Guy: In "Back to the Pilot", Brian uses Stewie's time machine to prevent the terrorist attacks of September 11, 2001. As a result, because that the Iraq War never happened, George W. Bush loses the 2004 election and starts a second Confederacy, leading to a nuclear Civil War with a death toll of 30 million. The two go back to stop Past!Brian from using the time machine... except Prime!Brian then uses it to make himself the author of the Harry Potter books.
Stewie: We did it, Brian! We made 9/11 happen!
[they jump in the air and high-five, then realize that they've just done]
Stewie: That probably wouldn't look good out of context.
- Our Friend Martin: In this special, two middle-schoolers go back in time and bring a young Martin Luther King Jr. back with them so he wouldn't be assassinated as an adult, only to end up in an alternate timeline where their school is now segregated, in addition to other racial problems. In the end, Martin decides to go back to his own time to bring the nation together, even if it means he'll die for it one day.
- In the Grand Finale of Xiaolin Showdown, Omi travels to the past (after experiencing a Bad Future first) in order to prevent Hannibal Bean from turning Chase Young evil by replacing the Lao-Mang soup with normal pea soup. It works, but after traveling back to present, he discovers that Hannibal turned Master Monk Guan evil this time, Wuya is restored to her human form with her powers (whereas in the normal timeline, Chase restored her without her powers) the other Xiaolin monks work on a farm, Master Fung is trapped in the Yin-Yang World, and Jack Spicer is good, making this timeline far worse than the original one. In the end, they manage to restore Omi's timeline back to normal after the two Omis from different timelines interact.
- Kid vs. Kat: In the two-part episode "Kat To The Future", Coop travels back in time using Kat's time machine to stop Millie from finding and adopting him. He succeeds, but upon returning to the present, Coop finds the human race has been enslaved by Kat's alien race, including himself, his friends, family, and neighbors have become La Résistance, and Kat rules the Earth with Coop's house as his HQ. Luckily, Coop manages to restore the timeline to it's mostly original state by stopping himself from causing this future to happen.
- X-Men: In "Time Fugitives, Part 1", Bishop's home time of 2055 has been ravaged by a synthetic plague, so he travels back to the 1990s to prevent it. Bishop's interventions expose the creators of the plague and saves a few lives—but the X-Men all die in the process, and the vaccine for the plague is never invented, resulting in even more deaths than the original timeline. Meanwhile, in the even farther future of 3999, Cable sees the disastrous results of Bishop's changes and is horrified to realize the only way to save his future is to stop Bishop and let the plague ravage the past. However, in "Time Fugitives, Part 2", Cable manages to Take a Third Option. He intervenes to ensure that Wolverine specifically gets dosed with the plague. Wolverine's extreme Healing Factor allows him to recover almost immediately, and his antibodies allow the creations of the plague vaccine much sooner than in the original timeline.
- In American Dad!: "The Best Christmas Story Never Told", Stan gets annoyed with all the secularism of the holidays (The tree getting banned, Christmas now just referred to as the "holidays", etc) and blames Jane Fonda for it (long story short to his logic: She inspired hippies to grow up and be modern liberals). When he's visited by Michelle, a ghost of Christmas Past, he uses the opportunity to escape from his Yet Another Christmas Carol story to kill Jane then changes targets to Donald Sutherland who inspired her. As he's tracking him, he runs into Martin Scorsese and convinces him to stop doing drugs. Michelle and Francine manage to pull him back to the present only to find out the Soviets now rule the US. They find out Stan started a domino effect that, by keeping Martin from doing drugs, prevented him from directing Taxi Driver, this, in turn, didn't inspire John Hinckley Jr to assassinate Ronald Reagan to impress Jane, which prevented Reagen's popularity with the people during his election and lost to Walter Mondale who, in turn, immediately surrendered the U.S to the USSR as his first official act as president (If you haven't guessed, this is a very silly show). To fix it, they try to make Taxi Driver themselves but naturally fail. So Michelle opts to just have Stan do the assassination attempt himself, which he succeeds (albeit at the loss of the Brady Bill aka the gun wait law. Stan naturally doesn't have a problem with that).
- In Gravity Falls, "The Time Traveler's Pig", Dipper tries to impress Wendy while at a carnival and ends up beaning her in the eye due to a misplaced throw at a ball toss. He meets a time traveler, Blendin Blandin, and manages to swipe his time travel device (designed like a tape measure) so he can go back and try to do the ball toss attempt better, Mabel joining in so she can relive winning a pig she dubbed Waddles. After several failed attempts, he has Mabel help him manage an impressive shot but at the cost of Pacifica getting Waddles instead since Mabel helping Dipper prevents Mabel from going to the game booth early to do so. Mabel pleas with Dipper to go back in time and fix this but he refuses initially until he sees Mabel slip into depression when he travels a few weeks ahead in time. He relents, goes back and allows events to play out as intended though it works out in the end.