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* ''Series/ChouseiKantaiSazerX'' kicks off with LaResistance traveling back in time to stop the formation of TheEmpire, by preventing their ancestors -- a rag-tag group of SpacePirates -- from conquering Earth.
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* This is Desmond's major character motivation throughout the third season of ''Series/{{Lost}}'' (apart from his desire to be reunited with his lost love Penny).
* In the series ''Series/MirrorMirror'', there is exactly ''one'' person who was trained to do this exactly ''once'', as revealed in the final episode. Everything prior to this point had already happened in her mentor's past.
* The ''Series/MysteriousWays'' episode "Yesterday" deals with a police officer who relives the previous day after accidentally shooting and killing his partner and praying for some way to make it right.
* In the ''Series/MysteryScienceTheater3000'' episode "[[Recap/MysteryScienceTheater3000S08E21TimeChasers Time Chasers]]", Crow decides to go back in time and convinces Mike to abandon his job at a Wisconsin cheese factory and be a rock star. This causes Mike to not get sent up to the Satellite of Love as he ends up dying due to a poorly timed crowd surf attempt. In his place is his angry chain-smoking brother Eddie. Crow gets fed up with how much Eddie attacks them and goes back to stop himself from convincing Mike.

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* %%* ''Series/{{Lost}}'': This is Desmond's major character motivation throughout the third season of ''Series/{{Lost}}'' (apart season, apart from his desire to be reunited with his lost love Penny).
Penny.
* In the series ''Series/MirrorMirror'', there ''Series/MirrorMirror1995'': There is exactly ''one'' person who was trained to do this exactly ''once'', as revealed in the final episode. Everything prior to this point had already happened in her mentor's past.
* The ''Series/MysteriousWays'' episode ''Series/MysteriousWays'': "Yesterday" deals with a police officer who relives the previous day after accidentally shooting and killing his partner and praying for some way to make it right.
* ''Series/MysteryScienceTheater3000'': In the ''Series/MysteryScienceTheater3000'' episode "[[Recap/MysteryScienceTheater3000S08E21TimeChasers Time Chasers]]", Crow decides to go back in time and convinces Mike to abandon his job at a Wisconsin cheese factory and be a rock star. This causes Mike to not get sent up to the Satellite of Love as he ends up dying due to a poorly timed crowd surf attempt. In his place is his angry chain-smoking brother Eddie. Crow gets fed up with how much Eddie attacks them and goes back to stop himself from convincing Mike.



** In "[[Recap/TheOuterLimits1995S2E1AStitchInTime A Stitch in Time]]", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "[[Recap/TheOuterLimits1995S6E21FinalAppealPartOne Final]] [[Recap/TheOuterLimits1995S6E22FinalAppealPartTwo Appeal]]", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).
** In "[[Recap/TheOuterLimits1995S6E13Decompression Decompression]]", a popular presidential candidate traveling on a plane and seeing an intangible image of a woman claiming to be from a BadFuture where his plane crashed (because of another time traveler's accidental interefence), and his ineffectual opponent ended up winning. She convinces him to jump out of the plane by claiming that she will use future technology to halt his fall moments before hitting the ground. This appears to happen, but then she explains that she is here to kill ''him'', as he is the one who will become PresidentEvil due to his paranoia. The falling scene repeats, and nobody catches him this time. The plane lands without problems. For bonus points, he's played by Creator/BruceBoxleitner, who plays a ''good'' president in ''Series/BabylonFive''.
** In "[[Recap/TheOuterLimits1995S7E2PatientZero Patient Zero]]", a time-traveling assassin killing certain people with a fast-acting poison before the strains of viruses they're carrying can combine in Patient Zero and start a pandemic that will kill most of humanity. Each time he goes back and is told that nothing has changed. He eventually realizes that he has to kill Patient Zero, who turns out to be a pretty woman, and he hesitates, resolving to prevent her from contacting the people with the strains. At the end of the episode, a colleague of his goes back in time and explains that the ''assassin'' is the one who is now Patient Zero, as his attempts to keep her away from the infected resulted in him creating the plague within himself. He voluntarily lets himself be poisoned in order to keep his future family safe.
** In "[[Recap/TheOuterLimits1995S6E5BreakingPoint Breaking Point]]", a scientist builds a time machine and uses it to go two days into the future. There, he sees his wife dying from a gunshot wound. He goes back and desperately tries to ensure his wife's safety. Unfortunately, a side effect of time travel is his increasingly slipping sanity. In the end, he is the one who ends up shooting her two days later. In a state of MyGodWhatHaveIDone, he jumps back to the day he originally met her and kills his past self, himself erased out of existence. Unfortunately, the last shot is of the girl, who would have become his wife, clearly depressed, about to pop some pills with alcohol, possibly resulting in her death.

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** In "[[Recap/TheOuterLimits1995S2E1AStitchInTime A Stitch in Time]]", a Time]]": A scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "[[Recap/TheOuterLimits1995S6E21FinalAppealPartOne Final]] [[Recap/TheOuterLimits1995S6E22FinalAppealPartTwo Appeal]]", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).
** In "[[Recap/TheOuterLimits1995S6E13Decompression Decompression]]", a Decompression]]": A popular presidential candidate traveling on a plane and seeing an intangible image of a woman claiming to be from a BadFuture where his plane crashed (because of another time traveler's accidental interefence), and his ineffectual opponent ended up winning. She convinces him to jump out of the plane by claiming that she will use future technology to halt his fall moments before hitting the ground. This appears to happen, but then she explains that she is here to kill ''him'', as he is the one who will become PresidentEvil due to his paranoia. The falling scene repeats, and nobody catches him this time. The plane lands without problems. For bonus points, he's played by Creator/BruceBoxleitner, who plays a ''good'' president in ''Series/BabylonFive''.
** In "[[Recap/TheOuterLimits1995S7E2PatientZero Patient Zero]]", a Zero]]": A time-traveling assassin killing certain people with a fast-acting poison before the strains of viruses they're carrying can combine in Patient Zero and start a pandemic that will kill most of humanity. Each time he goes back and is told that nothing has changed. He eventually realizes that he has to kill Patient Zero, who turns out to be a pretty woman, and he hesitates, resolving to prevent her from contacting the people with the strains. At the end of the episode, a colleague of his goes back in time and explains that the ''assassin'' is the one who is now Patient Zero, as his attempts to keep her away from the infected resulted in him creating the plague within himself. He voluntarily lets himself be poisoned in order to keep his future family safe.
** In "[[Recap/TheOuterLimits1995S6E5BreakingPoint Breaking Point]]", a Point]]": A scientist builds a time machine and uses it to go two days into the future. There, he sees his wife dying from a gunshot wound. He goes back and desperately tries to ensure his wife's safety. Unfortunately, a side effect of time travel is his increasingly slipping sanity. In the end, he is the one who ends up shooting her two days later. In a state of MyGodWhatHaveIDone, he jumps back to the day he originally met her and kills his past self, himself erased out of existence. Unfortunately, the last shot is of the girl, who would have become his wife, clearly depressed, about to pop some pills with alcohol, possibly resulting in her death.
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trope was cut/disambiguated due to cleanup


** In "[[Recap/StarTrekTheNextGenerationS6E14Tapestry Tapestry]]", Q gives Picard the opportunity to avoid a BarBrawl in which he suffered a near-fatal wound to his heart, leading to getting an artificial heart that failed him in the beginning of the episode. However, Picard finds that [[ForWantOfANail not being in the brawl drastically changed his future, as he's not a legendary captain, but a lowly lieutenant]].

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** In "[[Recap/StarTrekTheNextGenerationS6E14Tapestry Tapestry]]", Q gives Picard the opportunity to avoid a BarBrawl in which he suffered a near-fatal wound to his heart, leading to getting an artificial heart that failed him in the beginning of the episode. However, Picard finds that [[ForWantOfANail [[ButterflyOfDoom not being in the brawl drastically changed his future, as he's not a legendary captain, but a lowly lieutenant]].
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* ''Series/TheTwilightZone1985'': In "Time and Teresa Golowitz", Bluestone abandons his plan to have sex with Mary Ellen Cosgrove and instead prevents the title character from [[DrivenToSuicide committing suicide]] in October 1948. In the altered history, she becomes a highly successful singer. The Prince of Darkness admits that this was his plan all along as he is a sculptor of possibilities who could not bear the idea of the world losing a talent like Teresa's at 16.

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* ''Series/TheTwilightZone1985'': In "Time "[[Recap/TheTwilightZone1985S2E10 Time and Teresa Golowitz", Golowitz]]", Bluestone abandons his plan to have sex with Mary Ellen Cosgrove and instead prevents the title character from [[DrivenToSuicide committing suicide]] in October 1948. In the altered history, she becomes a highly successful singer. The Prince of Darkness admits that this was his plan all along as he is a sculptor of possibilities who could not bear the idea of the world losing a talent like Teresa's at 16.
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* The main plot of the first three seasons of ''Series/{{Heroes}}'', though this is more of a case of Set Right What Will Go Wrong. Name dropped by Hiro in Season 5's "[=PassFail=]" during his all-in-his-coma-mind-trial, and Mental!Adam/Kensei rightfully points out that he's simply reciting the opening to ''Quantum Leap''.

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* The main plot of the first three seasons of ''Series/{{Heroes}}'', though this is more of a case of Set Right What Will Go Wrong. Name dropped by Hiro in Season 5's 4's "[=PassFail=]" during his all-in-his-coma-mind-trial, and Mental!Adam/Kensei rightfully points out that he's simply reciting the opening to ''Quantum Leap''.

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* ''Series/Charmed1998'':
** "[[Recap/CharmedS1E17That70sEpisode That 70s Episode]]": When circumstances send Prue, Piper and Phoebe back in time to a point when their mother is pregnant with Phoebe, Phoebe attempts to take advantage of the situation to warn Patty of her impending death. However, although she goes so far as to write her mother a letter with a warning, Phoebe ultimately takes the letter back with her out of concern for the rest of the timeline.
** "[[Recap/CharmedS5E8AWitchInTime A Witch in Time]]" has a tragic example of this after Phoebe's latest vision saves the life of Miles, her current love interest, only for the sisters to later learn that Miles was meant to die; Phoebe's vision was due to her close emotional connection to Miles, but his death has to happen as it's part of the Grand Design. When a warlock from the future takes advantage of this disruption to come back to the present and kills Phoebe and Paige, ultimately the only way for Piper to save her sisters is to use the same temporal rift the warlock used to come back to go back to the day before and convince her past self to let Miles die.
** "[[Recap/CharmedS8E22ForeverCharmed Forever Charmed]]" has Piper go back to undo the events of the final battle that led to the deaths of her sisters.



** [[Recap/DoctorWhoS2E9TheTimeMeddler "The Time Meddler"]]: This how the Monk in sees his own actions: that by reversing the outcome of the Battle of Hastings, he would ensure that England gets a better king — Harold — than the one it actually got — William. The Doctor, however, is outraged by the sheer recklessness of this action.

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** [[Recap/DoctorWhoS2E9TheTimeMeddler "The "[[Recap/DoctorWhoS2E9TheTimeMeddler The Time Meddler"]]: Meddler]]": This how the Monk in sees his own actions: that by reversing the outcome of the Battle of Hastings, he would ensure that England gets a better king — Harold — than the one it actually got — William. The Doctor, however, is outraged by the sheer recklessness of this action.



** Possibly subverted in [[Recap/DoctorWhoS21E4ResurrectionOfTheDaleks "Resurrection of the Daleks"]], where the Daleks used the Doctor's interference in their creation to justify an attack on Gallifrey.

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** Possibly subverted in [[Recap/DoctorWhoS21E4ResurrectionOfTheDaleks "Resurrection "[[Recap/DoctorWhoS21E4ResurrectionOfTheDaleks Resurrection of the Daleks"]], Daleks]]", where the Daleks used the Doctor's interference in their creation to justify an attack on Gallifrey.



** This doesn't work in the Whoniverse all the time. The Series 1 episode [[Recap/DoctorWhoS27E8FathersDay "Father's Day"]] establishes that some points in time can't be changed (known as fixed points, they are usually major historical events but they could be more personal ones) without causing disaster, but other points are in flux and can be changed to varying degrees.
** [[Recap/DoctorWhoS30E11TurnLeft "Turn Left"]]: At the climax, Donna has to travel back in time to prevent a nightmarish alternate timeline from ever happening by ensuring that she makes the decision that leads to her meeting the Doctor.
** Amy gets a chance to do it in a small way in [[Recap/DoctorWhoS31E13TheBigBang "The Big Bang"]] — not by time travelling, but because [[spoiler:the universe is being rebooted from her memories, so if she remembers something the way it was, she can have it back]].
** [[Recap/DoctorWhoS32E10TheGirlWhoWaited "The Girl Who Waited"]] deconstructs this, in part. Amy gets trapped in a hospital that runs on NarniaTime, causing Rory arrive thirty-six years later, during which time she's been [[FutureBadass fighting robots]] with no living company. There's an opportunity to set things right, but Amy is not on board:

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** This doesn't work in the Whoniverse all the time. The Series 1 episode [[Recap/DoctorWhoS27E8FathersDay "Father's Day"]] "[[Recap/DoctorWhoS27E8FathersDay Father's Day]]" establishes that some points in time can't be changed (known as fixed points, they are usually major historical events but they could be more personal ones) without causing disaster, but other points are in flux and can be changed to varying degrees.
** [[Recap/DoctorWhoS30E11TurnLeft "Turn Left"]]: "[[Recap/DoctorWhoS30E11TurnLeft Turn Left]]": At the climax, Donna has to travel back in time to prevent a nightmarish alternate timeline from ever happening by ensuring that she makes the decision that leads to her meeting the Doctor.
** Amy gets a chance to do it in a small way in [[Recap/DoctorWhoS31E13TheBigBang "The "[[Recap/DoctorWhoS31E13TheBigBang The Big Bang"]] Bang]]" — not by time travelling, but because [[spoiler:the universe is being rebooted from her memories, so if she remembers something the way it was, she can have it back]].
** [[Recap/DoctorWhoS32E10TheGirlWhoWaited "The "[[Recap/DoctorWhoS32E10TheGirlWhoWaited The Girl Who Waited"]] Waited]]" deconstructs this, in part. Amy gets trapped in a hospital that runs on NarniaTime, causing Rory arrive thirty-six years later, during which time she's been [[FutureBadass fighting robots]] with no living company. There's an opportunity to set things right, but Amy is not on board:



** The Series 9 opening two-parter [[Recap/DoctorWhoS35E1TheMagiciansApprentice "The Magician's Apprentice"]]/[[Recap/DoctorWhoS35E2TheWitchsFamiliar "The Witch's Familiar"]] hinges on the Doctor getting a chance to fix a huge mistake he made: [[spoiler:abandoning a young, frightened Davros — who would create the Daleks as an adult — on a Skaro battlefield instead of saving his life, which likely started him on the path to evil]]. The problem is, ''how'' will the Doctor fix the mistake at a point when he has nothing to lose: [[spoiler:save him and risk the Daleks, or kill him and risk his own soul and the universe's stability]]?

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** The Series 9 opening two-parter [[Recap/DoctorWhoS35E1TheMagiciansApprentice "The "[[Recap/DoctorWhoS35E1TheMagiciansApprentice The Magician's Apprentice"]]/[[Recap/DoctorWhoS35E2TheWitchsFamiliar "The Apprentice]]"/"[[Recap/DoctorWhoS35E2TheWitchsFamiliar The Witch's Familiar"]] Familiar]]" hinges on the Doctor getting a chance to fix a huge mistake he made: [[spoiler:abandoning a young, frightened Davros — who would create the Daleks as an adult — on a Skaro battlefield instead of saving his life, which likely started him on the path to evil]]. The problem is, ''how'' will the Doctor fix the mistake at a point when he has nothing to lose: [[spoiler:save him and risk the Daleks, or kill him and risk his own soul and the universe's stability]]?



** [[Recap/DoctorWhoS37E3Rosa "Rosa"]]: In order to prevent the antagonist, a racist from the far future who is trying to derail the Civil Rights Movement, from succeeding, the Doctor and her friends practically have to bend over backwards to ensure that Rosa Parks is asked to give up her bus seat. Culminating in the Doctor, Graham and Yaz having to ''stay'' on the bus to ensure there are enough "white" passengers for this to happen.

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** [[Recap/DoctorWhoS37E3Rosa "Rosa"]]: "[[Recap/DoctorWhoS37E3Rosa Rosa]]": In order to prevent the antagonist, a racist from the far future who is trying to derail the Civil Rights Movement, from succeeding, the Doctor and her friends practically have to bend over backwards to ensure that Rosa Parks is asked to give up her bus seat. Culminating in the Doctor, Graham and Yaz having to ''stay'' on the bus to ensure there are enough "white" passengers for this to happen.
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* In ''Series/TheLazarusProject'', the titular organization uses time travel to go back in time before catastrophic events and alter the course of those events so that the world survives. In the first episode, they work to prevent ThePlague and then later try and stop one of their former members from setting off a nuclear warhead in Paris.
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* The conclusion of the ''Series/StarTrekVoyager'' "Year of Hell" serial. Or for that matter, the conclusion to the series altogether.

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* The conclusion of the ''Series/StarTrekVoyager'' "Year "[[Recap/StarTrekVoyagerS4E8YearOfHell Year of Hell" Hell]]" serial. Or for that matter, [[Recap/StarTrekVoyagerS7E23Endgame the conclusion to the series altogether.altogether]].
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** In "[[Recap/TheOuterLimits1995S2E1AStitchInTime A Stitch in Time]]", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "Final Appeal", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).

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** In "[[Recap/TheOuterLimits1995S2E1AStitchInTime A Stitch in Time]]", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "Final Appeal", "[[Recap/TheOuterLimits1995S6E21FinalAppealPartOne Final]] [[Recap/TheOuterLimits1995S6E22FinalAppealPartTwo Appeal]]", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).

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* ''Series/SevenDays'' is entirely about this trope: a time machine allows a government agent to go seven days back in time in order to prevent the catastrophe of the week from taking place. Most episodes only deal with the time span of a week, due to the limitations of the time machine. However, several episodes involve the arrival of more advanced time machines from years in the future. In the first case, a time travel tries to stop a woman from developing a cure for cancer, which is going to mutate and start a pandemic. He succeeds but is killed himself. In another, a man arrives, claiming that a Muslim religious leader is secretly a radical, who will start the bloodiest religious war in history. It turns out the time traveler is himself a radical (or, possibly, someone not even human), who intends to kick-start just such a war by killing the imam.

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* ''Series/SevenDays'' ''Series/SevenDays1998'' is entirely about this trope: a time machine allows a government agent to go seven days back in time in order to prevent the catastrophe of the week from taking place. Most episodes only deal with the time span of a week, due to the limitations of the time machine. However, several episodes involve the arrival of more advanced time machines from years in the future. In the first case, a time travel tries to stop a woman from developing a cure for cancer, which is going to mutate and start a pandemic. He succeeds but is killed himself. In another, a man arrives, claiming that a Muslim religious leader is secretly a radical, who will start the bloodiest religious war in history. It turns out the time traveler is himself a radical (or, possibly, someone not even human), who intends to kick-start just such a war by killing the imam.



* ''Series/TheUmbrellaAcademy'' is driven by this trope. In the very first episode, Number Five reveals that he has returned to 2019 in order to prevent a coming apocalypse. In season two, this is again Five's motivation, while Klaus has a plan to [[spoiler: prevent his lover Dave, who he met when he accidentally time traveled to the Vietnam War in season one, from enlisting in the army, as this will likely lead to his death]].

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* ''Series/TheUmbrellaAcademy'' ''Series/TheUmbrellaAcademy2019'' is driven by this trope. In the very first episode, Number Five reveals that he has returned to 2019 in order to prevent a coming apocalypse. In season two, this is again Five's motivation, while Klaus has a plan to [[spoiler: prevent [[spoiler:prevent his lover Dave, who he met when he accidentally time traveled time-traveled to the Vietnam War in season one, from enlisting in the army, as this will likely lead to his death]].



* ''Series/{{Farscape}}''
** Subverted in episode "Different Destinations", where the team go back in time to a historic siege and make things ''worse'' by getting everyone except them killed.
** Played straight in "Kansas" when the team accidentally goes back to Earth in 1985 and has to prevent John's father from going on the Space Shuttle ''Challenger'' to prevent his death and John possibly never ending up on Moya.

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* ''Series/{{Farscape}}''
''Series/{{Farscape}}'':
** Subverted in episode "Different Destinations", "[[Recap/FarscapeS03E05DifferentDestinations ...Different Destinations]]", where the team go back in time to a historic siege and make things ''worse'' by getting everyone except them killed.
** Played straight in "Kansas" "[[Recap/FarscapeS04E12Kansas Kansas]]" when the team accidentally goes back to Earth in 1985 and has to prevent John's father from going on the Space Shuttle ''Challenger'' to prevent his death and John possibly never ending up on Moya.



* Naturally, ''Series/{{Life On Mars|2006}}'' and ''Series/AshesToAshes2008'' have played with this: in Sam's case, it was finding out why his father abandoned him, as well as arresting the serial killer who'd kidnapped his girlfriend and a crime lord who'd had a witness in his custody murdered; in Alex's, it was preventing her parents' death by car bomb. Their success rates are... varied; Sam eventually wound up ''convincing'' his father to skip town, because there was that little matter of a murder and racketeering charge if he stayed...

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* Naturally, ''Series/{{Life On Mars|2006}}'' ''Series/LifeOnMars2006'' and ''Series/AshesToAshes2008'' have played with this: in Sam's case, it was finding out why his father abandoned him, as well as arresting the serial killer who'd kidnapped his girlfriend and a crime lord who'd had a witness in his custody murdered; in Alex's, it was preventing her parents' death by car bomb. Their success rates are... varied; Sam eventually wound up ''convincing'' his father to skip town, because there was that little matter of a murder and racketeering charge if he stayed...



* In the ''Series/MysteryScienceTheater3000'' episode featuring the film ''Film/TimeChasers'', Crow decides to go back in time and convinces Mike to abandon his job at a Wisconsin cheese factory and be a rock star. This causes Mike to not get sent up to the Satellite of Love as he ends up dying due to a poorly timed crowd surf attempt. In his place is his angry chain-smoking brother Eddie. Crow gets fed up with how much Eddie attacks them and goes back to stop himself from convincing Mike.
* In ''Series/TheOrville'' episode "Pria", the titular captain turns out to be a time traveler from the 29th century, who retrieves and sells unique objects, which have historically been destroyed. In this case, she saves the ''Orville'' from a NegativeSpaceWedgie, which was supposed to destroy the ship with all hands. She hijacks the ship and takes it through a wormhole into the future, but the crew manages to make it back. Ed has the wormhole destroyed, which {{Ret Gone}}s Pria, but somehow allows the ''Orville'' to survive anyway. Also used as a joke in the pilot, where Ed asks if a time-acceleration device can be used in reverse to, for example, go back a few years and prevent him from marrying his ex-wife (and XO) Kelly. [[spoiler:That ends up being the plot of the season two finale two-parter]].
* ''Series/TheOuterLimits1963'' episode "The Man Who Was Never Born". A mutant from a devastated future goes back in time to prevent the biological disaster that destroyed civilization.

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* In the ''Series/MysteryScienceTheater3000'' episode featuring the film ''Film/TimeChasers'', "[[Recap/MysteryScienceTheater3000S08E21TimeChasers Time Chasers]]", Crow decides to go back in time and convinces Mike to abandon his job at a Wisconsin cheese factory and be a rock star. This causes Mike to not get sent up to the Satellite of Love as he ends up dying due to a poorly timed crowd surf attempt. In his place is his angry chain-smoking brother Eddie. Crow gets fed up with how much Eddie attacks them and goes back to stop himself from convincing Mike.
* ''Series/TheOrville'': In ''Series/TheOrville'' the episode "Pria", "[[Recap/TheOrvilleS1E05Pria Pria]]", the titular captain turns out to be a time traveler from the 29th century, who retrieves and sells unique objects, which have historically been destroyed. In this case, she saves the ''Orville'' from a NegativeSpaceWedgie, which was supposed to destroy the ship with all hands. She hijacks the ship and takes it through a wormhole into the future, but the crew manages to make it back. Ed has the wormhole destroyed, which {{Ret Gone}}s Pria, but somehow allows the ''Orville'' to survive anyway. Also used as a joke in the pilot, where Ed asks if a time-acceleration device can be used in reverse to, for example, go back a few years and prevent him from marrying his ex-wife (and XO) Kelly. [[spoiler:That ends up being the plot of the season two finale two-parter]].
* ''Series/TheOuterLimits1963'' ''Series/TheOuterLimits1963'': In the episode "The "[[Recap/TheOuterLimits1963S1E6TheManWhoWasNeverBorn The Man Who Was Never Born". A Born]]", a mutant from a devastated future goes back in time to prevent the biological disaster that destroyed civilization.



** In "A Stitch In Time", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "Final Appeal", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).
** In "Decompression", a popular presidential candidate traveling on a plane and seeing an intangible image of a woman claiming to be from a BadFuture where his plane crashed (because of another time traveler's accidental interefence), and his ineffectual opponent ended up winning. She convinces him to jump out of the plane by claiming that she will use future technology to halt his fall moments before hitting the ground. This appears to happen, but then she explains that she is here to kill ''him'', as he is the one who will become PresidentEvil due to his paranoia. The falling scene repeats, and nobody catches him this time. The plane lands without problems. For bonus points, he's played by Bruce Boxleitner, who plays a ''good'' president in ''Series/BabylonFive''.
** In "Patient Zero", a time-traveling assassin killing certain people with a fast-acting poison before the strains of viruses they're carrying can combine in Patient Zero and start a pandemic that will kill most of humanity. Each time he goes back and is told that nothing has changed. He eventually realizes that he has to kill Patient Zero, who turns out to be a pretty woman, and he hesitates, resolving to prevent her from contacting the people with the strains. At the end of the episode, a colleague of his goes back in time and explains that the ''assassin'' is the one who is now Patient Zero, as his attempts to keep her away from the infected resulted in him creating the plague within himself. He voluntarily lets himself be poisoned in order to keep his future family safe.
** In "Breaking Point", a scientist builds a time machine and uses it to go two days into the future. There, he sees his wife dying from a gunshot wound. He goes back and desperately tries to ensure his wife's safety. Unfortunately, a side effect of time travel is his increasingly slipping sanity. In the end, he is the one who ends up shooting her two days later. In a case of WhatHaveIDone, he jumps back to the day he originally met her and kills his past self, himself erased out of existence. Unfortunately, the last shot is of the girl, who would have become his wife, clearly depressed, about to pop some pills with alcohol, possibly resulting in her death.

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** In "A "[[Recap/TheOuterLimits1995S2E1AStitchInTime A Stitch In Time", in Time]]", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "Final Appeal", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).
** In "Decompression", "[[Recap/TheOuterLimits1995S6E13Decompression Decompression]]", a popular presidential candidate traveling on a plane and seeing an intangible image of a woman claiming to be from a BadFuture where his plane crashed (because of another time traveler's accidental interefence), and his ineffectual opponent ended up winning. She convinces him to jump out of the plane by claiming that she will use future technology to halt his fall moments before hitting the ground. This appears to happen, but then she explains that she is here to kill ''him'', as he is the one who will become PresidentEvil due to his paranoia. The falling scene repeats, and nobody catches him this time. The plane lands without problems. For bonus points, he's played by Bruce Boxleitner, Creator/BruceBoxleitner, who plays a ''good'' president in ''Series/BabylonFive''.
** In "Patient Zero", "[[Recap/TheOuterLimits1995S7E2PatientZero Patient Zero]]", a time-traveling assassin killing certain people with a fast-acting poison before the strains of viruses they're carrying can combine in Patient Zero and start a pandemic that will kill most of humanity. Each time he goes back and is told that nothing has changed. He eventually realizes that he has to kill Patient Zero, who turns out to be a pretty woman, and he hesitates, resolving to prevent her from contacting the people with the strains. At the end of the episode, a colleague of his goes back in time and explains that the ''assassin'' is the one who is now Patient Zero, as his attempts to keep her away from the infected resulted in him creating the plague within himself. He voluntarily lets himself be poisoned in order to keep his future family safe.
** In "Breaking Point", "[[Recap/TheOuterLimits1995S6E5BreakingPoint Breaking Point]]", a scientist builds a time machine and uses it to go two days into the future. There, he sees his wife dying from a gunshot wound. He goes back and desperately tries to ensure his wife's safety. Unfortunately, a side effect of time travel is his increasingly slipping sanity. In the end, he is the one who ends up shooting her two days later. In a case state of WhatHaveIDone, MyGodWhatHaveIDone, he jumps back to the day he originally met her and kills his past self, himself erased out of existence. Unfortunately, the last shot is of the girl, who would have become his wife, clearly depressed, about to pop some pills with alcohol, possibly resulting in her death.



** Subverted in "The Gamekeeper": Jack and Daniel ''think'' that they're being sent to the past to fix mistakes in their lives, but it turns out that they're just mentally reliving them, not really time travelling, and there's no way for them to fix it anyways.
** Played straight in the Aschen arc, in the episodes "2010" and "2001". The former takes place in a BadFuture, where the Aschen, posing as benevolent aliens, infect Earth with a sterility vaccine that will eventually cause its population to die out. To avert it, SG-1 sends a [[NoteToSelf note to their past selves]] back in time, leading to a less tragic future.
** Played straight in the two-parter "Moebius" when an attempt to go back in time to retrieve a piece of technology results in screwing up the timeline and having to go back in time again to fix it.

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** Subverted in "The Gamekeeper": "[[Recap/StargateSG1S2E4TheGamekeeper The Gamekeeper]]": Jack and Daniel ''think'' that they're being sent to the past to fix mistakes in their lives, but it turns out that they're just mentally reliving them, not really time travelling, and there's no way for them to fix it anyways.
** Played straight in the Aschen arc, in the episodes "2010" "[[Recap/StargateSG1S4E162010 2010]]" and "2001"."[[Recap/StargateSG1S5E102001 2001]]". The former takes place in a BadFuture, where the Aschen, posing as benevolent aliens, infect Earth with a sterility vaccine that will eventually cause its population to die out. To avert it, SG-1 sends a [[NoteToSelf note to their past selves]] back in time, leading to a less tragic future.
** Played straight in the two-parter "Moebius" "[[Recap/StargateSG1S8E19MoebiusPart1 Moebius, Part 1]]/[[Recap/StargateSG1S8E20MoebiusPart2 Part 2]]" when an attempt to go back in time to retrieve a piece of technology results in screwing up the timeline and having to go back in time again to fix it.



* The ''Series/StargateAtlantis'' episode "The Last Man" has Sheppard thrown 48,000 years into the future, where a program Rodney left behind recounts a long FromBadToWorse story of the intervening years and arranges to send Sheppard back to fix everything. He even gives Sheppard some crucial information, like Teyla's location at the time, so Sheppard can change what happened for the better.

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* The ''Series/StargateAtlantis'' episode "The "[[Recap/StargateAtlantisS04E20TheLastMan The Last Man" Man]]" has Sheppard thrown 48,000 years into the future, where a program Rodney left behind recounts a long FromBadToWorse story of the intervening years and arranges to send Sheppard back to fix everything. He even gives Sheppard some crucial information, like Teyla's location at the time, so Sheppard can change what happened for the better.



* Guinan of ''Series/StarTrekTheNextGeneration'' is practically this trope walking personified (as for reasons that were never even hinted at until TheMovie, changes in the timeline do not affect her), especially in "Yesterday's Enterprise". More technically they don't entirely affect her. She could identify something was wrong, but didn't know what could have caused it.
** In "Tapestry", Q gives Picard the opportunity to avoid a BarBrawl in which he suffered a near-fatal wound to his heart, leading to getting an artificial heart that failed him in the beginning of the episode. [[ForWantOfANail Picard however finds that not being in the brawl drastically changed his future, as he's not a legendary captain, but a lowly lieutenant.]]
* The iconic ''[[Series/StarTrekTheOriginalSeries TOS]]'' episode "The City on the Edge of Forever": We see what's happened when [=McCoy=] goes through the Guardian: Edith Keeler starts a revolution, causing the Germans to win WWII, causing havoc and destruction throughout the timeline. Kirk and Spock must enter and make sure Keeler dies like she's supposed to. Of course, a little thing called love gets in the way...

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* ''Series/StarTrekTheNextGeneration'':
**
Guinan of ''Series/StarTrekTheNextGeneration'' is practically this trope walking personified (as for reasons that were never even hinted at until TheMovie, changes in the timeline do not affect her), especially in "Yesterday's Enterprise"."[[Recap/StarTrekTheNextGenerationS3E15YesterdaysEnterprise Yesterday's Enterprise]]". More technically they don't entirely affect her. She could identify something was wrong, but didn't know what could have caused it.
** In "Tapestry", "[[Recap/StarTrekTheNextGenerationS6E14Tapestry Tapestry]]", Q gives Picard the opportunity to avoid a BarBrawl in which he suffered a near-fatal wound to his heart, leading to getting an artificial heart that failed him in the beginning of the episode. However, Picard finds that [[ForWantOfANail Picard however finds that not being in the brawl drastically changed his future, as he's not a legendary captain, but a lowly lieutenant.]]
lieutenant]].
* The iconic ''[[Series/StarTrekTheOriginalSeries TOS]]'' ''Series/StarTrekTheOriginalSeries'' episode "The "[[Recap/StarTrekS1E28TheCityOnTheEdgeOfForever The City on the Edge of Forever": Forever]]". We see what's happened when [=McCoy=] goes through the Guardian: Edith Keeler starts a revolution, causing the Germans to win WWII, causing havoc and destruction throughout the timeline. Kirk and Spock must enter and make sure Keeler dies like she's supposed to. Of course, a little thing called love gets in the way...



* In the Season One finale of ''Series/StarTrekStrangeNewWorlds'', "A Quality of Mercy", [[spoiler:Pike attempts to ScrewDestiny by writing and convincing the future cadets to not be there the day he is meant to be hideously disfigured saving them. He is confronted by an alternate future ''Admiral'' Pike, who shows him that doing so will lead to a reignition of the Federation-Romulan War.]]

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* In the Season One finale of ''Series/StarTrekStrangeNewWorlds'', "A "[[Recap/StarTrekStrangeNewWorldsS1E10AQualityOfMercy A Quality of Mercy", Mercy]]", [[spoiler:Pike attempts to ScrewDestiny by writing and convincing the future cadets to not be there the day he is meant to be hideously disfigured saving them. He is confronted by an alternate future ''Admiral'' Pike, who shows him that doing so will lead to a reignition of the Federation-Romulan War.]]War]].



** In Season 2, A djinn grants Dean a wish and he wakes up in an alternate universe in which his mother never died and he and Sam never became hunters. Sam is happy but estranged from Dean who lives an ordinary life as a mechanic with a drinking problem. When Dean realizes that all the people that John, Sam, and Dean saved are dead, he sets out to restore the timeline by hunting the djinn. [[spoiler: It turns out he's in a MentalWorld created by the djinn not in an actual alternate timeline.]]
** In "In The Beginning", Dean ''thinks'' that his jump into the past is to set right what once went wrong (Castiel all but states it outright), but not only does it turn out he was only meant to ''witness'' what went wrong and not change it, it sure looks like he actually ''caused'' it. Castiel eventually makes it clear that it was a closed time loop and Dean can't fight fate.
** In "The End" Zachariah sends Dean to a BadFuture where Dean is a hardened guerrilla, Cas is a drug-addled sex guru and Sam has [[spoiler: said yes to Lucifer.]] Zachariah is trying to convince Dean to say yes to Michael, but Dean instead resolves to end his estrangement with Sam.
** "The Song Remains The Same" had an angel go back to that time to try to kill Sam and Dean's mother before they were born in order to stop the Apocalypse. While she seemingly succeeds in killing their father, he is brought back as a vessel for Archangel Michael, who kills the angel.
** {{Inverted}} in "My Heart Will Go On" the brothers find themselves in an alternate timeline where the ''Titanic'' never sank, Jo and Ellen are alive and Ellen is happily married to Bobby. Also, Music/CelineDion is a broke lounge singer and the boys drive a Mustang. It's arguably a better timeline than [[CrapsackWorld their own]] but it enrages the fates so the timeline must be set right.
** In "As Time Goes By", Henry wants to return to 1958 to stop Abaddon and be a father to John, but Dean fears that it'll have an unforeseen consequence and stops him by force. Although even Dean is taken aback when Henry points out that his return would mean that the Apocalypse and all the other [[SealedEvilInACan sealed evils]] that have killed thousands of people would never have been released.

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** In Season 2, A a djinn grants Dean a wish and he wakes up in an alternate universe in which his mother never died and he and Sam never became hunters. Sam is happy but estranged from Dean who lives an ordinary life as a mechanic with a drinking problem. When Dean realizes that all the people that John, Sam, and Dean saved are dead, he sets out to restore the timeline by hunting the djinn. [[spoiler: It turns out he's in a MentalWorld created by the djinn not in an actual alternate timeline.]]
** In "In The Beginning", "[[Recap/SupernaturalS04E03InTheBeginning In the Beginning]]", Dean ''thinks'' that his jump into the past is to set right what once went wrong (Castiel all but states it outright), but not only does it turn out he was only meant to ''witness'' what went wrong and not change it, it sure looks like he actually ''caused'' it. Castiel eventually makes it clear that it was a closed time loop and Dean can't fight fate.
** In "The End" "[[Recap/SupernaturalS05E04TheEnd The End]]", Zachariah sends Dean to a BadFuture where Dean is a hardened guerrilla, Cas is a drug-addled sex guru and Sam has [[spoiler: said [[spoiler:said yes to Lucifer.]] Lucifer]]. Zachariah is trying to convince Dean to say yes to Michael, but Dean instead resolves to end his estrangement with Sam.
** "The "[[Recap/SupernaturalS05E13TheSongRemainsTheSame The Song Remains The Same" had the Same]]" has an angel go back to that time to try to kill Sam and Dean's mother before they were born in order to stop the Apocalypse. While she seemingly succeeds in killing their father, he is brought back as a vessel for Archangel Michael, who kills the angel.
** {{Inverted}} {{Inverted|Trope}} in "My "[[Recap/SupernaturalS06E17MyHeartWillGoOn My Heart Will Go On" the On]]". The brothers find themselves in an alternate timeline where the ''Titanic'' never sank, Jo and Ellen are alive and Ellen is happily married to Bobby. Also, Music/CelineDion is a broke lounge singer and the boys drive a Mustang. It's arguably a better timeline than [[CrapsackWorld their own]] but it enrages the fates so the timeline must be set right.
** In "As "[[Recap/SupernaturalS08E12AsTimeGoesBy As Time Goes By", By]]", Henry wants to return to 1958 to stop Abaddon and be a father to John, but Dean fears that it'll have an unforeseen consequence and stops him by force. Although even Dean is taken aback when Henry points out that his return would mean that the Apocalypse and all the other [[SealedEvilInACan sealed evils]] that have killed thousands of people would never have been released.



* ''Series/TheXFiles'' episode "Synchrony" presents the case of a strange old man warning an MIT student and professor that the student is going to die at a specific time -- because of this warning the professor, attempting to save the student, ends up accidentally pushing him into the path of an oncoming bus and thus the warning is a SelfFulfillingProphecy. The old man is [[spoiler:actually the professor from the future, who has traveled back in time]] attempting to Set Right What Will Go Wrong and prevent an impending scientific breakthrough [[spoiler:that would be made by the professor in collaboration with his girlfriend, also a scientist, and the student, and which would be a catalyst for a catastrophic technological development.]] Mulder cites an old theory of Scully's about how YouCantFightFate, and so the old man's efforts are probably doomed. [[spoiler:Although the professor manages to kill both his present and future selves and erase all of his files, as the episode ends, the girlfriend is continuing the research on her own with backups of the erased data.]]
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* ''Series/TheXFiles'' ''Series/TheXFiles'': The episode "Synchrony" "[[Recap/TheXFilesS04E19Synchrony Synchrony]]" presents the case of a strange old man warning an MIT student and professor that the student is going to die at a specific time -- because of this warning the professor, attempting to save the student, ends up accidentally pushing him into the path of an oncoming bus and thus the warning is a SelfFulfillingProphecy. The old man is [[spoiler:actually the professor from the future, who has traveled back in time]] attempting to Set Right What Will Go Wrong and prevent an impending scientific breakthrough [[spoiler:that would be made by the professor in collaboration with his girlfriend, also a scientist, and the student, and which would be a catalyst for a catastrophic technological development.]] Mulder cites an old theory of Scully's about how YouCantFightFate, and so the old man's efforts are probably doomed. [[spoiler:Although the professor manages to kill both his present and future selves and erase all of his files, as the episode ends, the girlfriend is continuing the research on her own with backups of the erased data.]]
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* ''Series/StargateUniverse'' has a particularly complex example in "Time". The episode initially plays like FoundFootageFilms, as scene as recordings on a kino. It then becomes apparent the crew of ''Destiny'' found a kino that had been sent back in time on alien planet. The footage shows how the team was slaughtered by the local predators; but ''also'' reveals they (and as such the current ''Destiny'' crew as well) all have a fatal virus from tainted water, and the predator venom acts as cure. [[spoiler:In a rather brilliant twist, the first attempt to fix things ends in disaster with more deaths. The episode ends with Scott throwing another kino back in time, leaving a different version of ''Destiny'' to get it right.]]

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* ''Series/StargateUniverse'' has a particularly complex example in "Time". The episode initially plays like FoundFootageFilms, as scene with scenes as recordings on a kino. It then becomes apparent the crew of ''Destiny'' found a kino that had been sent back in time on alien planet. The footage shows how the team was slaughtered by the local predators; but ''also'' reveals they (and as such the current ''Destiny'' crew as well) all have a fatal virus from tainted water, and the predator venom acts as cure. [[spoiler:In a rather brilliant twist, the first attempt to fix things ends in disaster with more deaths. The episode ends with Scott throwing another kino back in time, leaving a different version of ''Destiny'' to get it right.]]
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[[folder:Series Plots]]
* The TropeNamer is ''Series/QuantumLeap'', whose entire plot is a series of these.
* ''Series/TruCalling'': Tru does this in almost every episode. A number of twists and variations of the trope are also used.
* This was also the plot for the entire ''Series/{{Voyagers}}'' series where Phineas and Jeffrey would travel through time to "give history a little nudge".
* Appears to be the premise of the lamentably late Creator/{{NBC}} series ''Series/{{Journeyman}}''.
** One episode revolves around him trying to undo something he did by accidentally leaving his digital camera in the 70s. He returns home to find that computer technology is decades ahead of what it was (holographic screens and video-newspapers are commonplace), but his son was never born (he was delayed at work due to a computer error), replaced instead by a daughter who was conceived a few days later. Despite his wife's objections, he goes back and fixes it.
** The pilot episode gave a clever twist to the usual formula: Dan initially concludes that the reason he keeps jumping back in time is to prevent Neal Gaines from committing suicide, but in the end he realizes that his real purpose was to prevent him from [[spoiler:committing murder.]]
* ''Series/OdysseyFive'', where a FiveManBand witnesses the destruction of Earth from a space shuttle and are sent back in time five years by SufficientlyAdvancedAliens to prevent it. Although they promise not to change events, each of them can't resist meddling with their past to make it better. For instance one woman who knows her son will die of cancer starts giving him a potentially dangerous preventative drug -- her husband, convinced she's going insane, cuts off her access to the boy. Another character bets on a football game -- the size of his bet leads to other people betting on the outcome, starting rumors that adversely affect the course of the game. Worse, the group have considered the possibility that their own actions might hasten, or even cause, the destruction of Earth.
* The short-lived Fox show ''Second Chance'' has a man dying in a crash in 2011 and finding he's "not good enough for Heaven but not bad enough for Hell." To decide his eternal fate, he's sent back in time to 1987 and trying to keep his younger self from some major mistakes.
** One episode has Charles realizing a friend is about to be killed in a drunk driving accident and getting his younger self, Chazz, to stop him from going out like that.
** Charles doesn't find anything wrong with how Chazz is constantly putting down a female classmate as a nerd. St. Peter (his angelic guide) brings Charles into the future to show how that treatment set the woman on a path to become a pathetic, single woman who's just been fired from her job at a diner. Charles gets Chazz to help the girl gain some self-confidence and even "glam up" for a date. St. Peter takes Charles back into the future to show the woman is now a strong, happily married mother who owns a chain of diners.
* ''Series/SevenDays'' is entirely about this trope: a time machine allows a government agent to go seven days back in time in order to prevent the catastrophe of the week from taking place. Most episodes only deal with the time span of a week, due to the limitations of the time machine. However, several episodes involve the arrival of more advanced time machines from years in the future. In the first case, a time travel tries to stop a woman from developing a cure for cancer, which is going to mutate and start a pandemic. He succeeds but is killed himself. In another, a man arrives, claiming that a Muslim religious leader is secretly a radical, who will start the bloodiest religious war in history. It turns out the time traveler is himself a radical (or, possibly, someone not even human), who intends to kick-start just such a war by killing the imam.
* The main plot of the first three seasons of ''Series/{{Heroes}}'', though this is more of a case of Set Right What Will Go Wrong. Name dropped by Hiro in Season 5's "[=PassFail=]" during his all-in-his-coma-mind-trial, and Mental!Adam/Kensei rightfully points out that he's simply reciting the opening to ''Quantum Leap''.
* Another example of this is the CBC drama, ''Series/BeingErica'', where the majority of episodes were centred around her travelling back to a point in her past where she tries to put right something, she believes, went wrong in her life. Normally it would turn out that actually she needed to learn a lesson from that event and her changes wouldn't help her life that much. [[spoiler:There were also a couple of episodes that varied from this format but stayed true to this theme. One where she was required to make changes to the life of the man sending her back in time, another where she managed to make a huge change in her life by stopping her brother's accidental death. This ended up to make her life drastically different and he still died but at a different time in his life and in a different way. Also, in another episode she had to travel forwards in time to learn about another time traveller's life as the version of him she knew in her present time was actually the past version of his actual self. He was refusing to make the changes he needed to and she had to convince him to make the changes he needed to and return to his own time.]]
* ''Series/{{Angel}}'' {{crossover}} episode "[[Recap/AngelS01E08IWillRememberYou I Will Remember You]]" is a crossover with ''Series/BuffyTheVampireSlayer'', which sees Angel become human after being exposed to the blood of a Mohra demon. However, realising that he cannot fight evil as a human and he will endanger Buffy if he remains a mortal man, Angel asks the Oracles- agents of the Powers That Be- to undo his current humanity, and in response they turn back time by twenty-four hours, leaving Angel's memory intact so that he can undo the events that took place.
* ''Series/Charmed1998'':
** The episode "[[Recap/CharmedS5E8AWitchInTime A Witch in Time]]" sees a tragic version of this; when Phoebe has a vision of her current love interest dying, the sisters only learn after they have saved his life that Miles is actually destined to die and Phoebe’s vision was due to her emotional connection to him. After Miles’ survival creates a temporal rift that allows a warlock from the future to steal the Book of Shadows and kill Phoebe and Paige, Piper’s only option is to use the rift herself and go back in time to stop her past self saving Miles in the first place.
** The sixth season sees the sisters have to deal with this on a larger scale; their new Whitelighter, Chris, is revealed to be their currently-unborn son/nephew from the future, who has come back to prevent the events that will lead to his older brother Wyatt turning to evil.
* ''Series/HerculesTheLegendaryJourneys'' has an interesting variation in the two-part episode "Armageddon Now" when villain Callisto is sent back in time by Hope to kill Hercules's mother to prevent his being born. While this is clearly an example of MakeWrongWhatOnceWentRight, Callisto agrees to commit the heinous act in exchange for the chance to [[spoiler:prevent her parents from being killed by Xena's army.]]
* The first season of the Israeli teen series ''The Island'' features the attempts of an underground group of time travellers trying to prevent [[ApocalypseHow a giant meteor wiping out most of humanity]] in (their) past in 2009 (two years after the series premiered). The second season features the series’ protagonists trying to undo a BadFuture, going back to (what later became) Israel in 1909, and the new BigBad. The third season features the protagonists going to mediaeval times to thwart him again.
* In ''Series/NineNineTimeTravels'', a KoreanDrama, Sun-woo wants to change history and gain revenge against the man who killed his father and ruined his family. Luckily, Sun-woo has nine incense sticks that allow him to travel through time.
* ''Series/LegendsOfTomorrow'' is all about a group of heroes and villains being brought together by a [[spoiler:[[ScrewTheRulesImDoingWhatsRight rogue]]]] time traveler in order to prevent a [[EvilerThanThou far worse villain]] from conquering the world in the future by defeating him in the past.
** Following Savage's defeat at the end of Season 1, the team dedicates themselves to stopping other time travelers from rewriting history for their own ends.
** Season 3 flips it around as the team's actions have caused massive ''breaks'' in time. Thus, they have to help fix the problems they themselves caused. And in Season 4, their actions help spread supernatural creatures across history.
** In Season 5, a group of evil souls are released from Hell to come BackFromTheDead in their own time periods, with orders to spread chaos across history. The Legends take a moment to celebrate that this time, the changes to history ''aren't'' their fault.
* ''Series/TwelveMonkeys'': Cole's mission throughout the series is to somehow prevent the release of the plague in 2017 that decimates most of humanity and brings the species to the brink of extinction by 2043.
* ''Series/KamenRiderKabuto'': The entire series' plot was a result of what Souji Tendou/Kabuto did in TheMovie. [[spoiler:TheMovie itself is set in an alternate future where Earth was in ruins after a large meteorite carrying Worms hit Earth 7 years before. After getting his hands on his SuperMode, Tendou goes back in time to alter the past, creating the timeline and plot set in the TV series.]]
* In the [[Creator/{{Syfy}} Sci-Fi Channel]] mini-series ''[=5ive=] Days to Midnight'', the protagonist is sent a futuristic briefcase by an unknown party, containing a police file on his murder [[WhoDunnitToMe to happen five days later]]. [[spoiler:At the end of the series he works out that his daughter, then ten years old, was the future owner of the briefcase, trying to avert his murder using time travel technology.]]
* In ''Series/TheCrossing'', TheConspiracy is a WellIntentionedExtremist plot employed by individuals who've come back to prevent a BadFuture. [[spoiler:The final scene of the WrapItUp episode (series was CutShort) suggest this may also be a SelfFulfillingProphecy.]]
* ''Series/TheOuterLimits1995'':
** In "A Stitch In Time", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "Final Appeal", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).
** In "Decompression", a popular presidential candidate traveling on a plane and seeing an intangible image of a woman claiming to be from a BadFuture where his plane crashed (because of another time traveler's accidental interference), and his ineffectual opponent ended up winning. She convinces him to jump out of the plane by claiming that she will use future technology to halt his fall moments before hitting the ground. This appears to happen, but then she explains that she is here to kill ''him'', as he is the one who will become PresidentEvil due to his paranoia. The falling scene repeats, and nobody catches him this time. The plane lands without problems.
** In "Patient Zero", a time-traveling assassin killing certain people with a fast-acting poison before the strains of viruses they're carrying can combine in Patient Zero and start a pandemic that will kill most of humanity. Each time he goes back and is told that nothing has changed. He eventually realizes that he has to kill Patient Zero, who turns out to be a pretty woman, and he hesitates, resolving to prevent her from contacting the people with the strains. At the end of the episode, a colleague of his goes back in time and explains that the ''assassin'' is the one who is now Patient Zero, as his attempts to keep her away from the infected resulted in him creating the plague within himself. He voluntarily lets himself be poisoned in order to keep his future family safe.
** In "Gettysburg", Nicholas Prentice seeks to alter history by convincing Andy Larouche that there is no glory in any war so he will not assassinate the U.S. President on November 19, 2013. He does so by sending him and his friend Vince Chance back to the eve of the Battle of Gettysburg in 1863. For his part, Andy tries to change history by saving the Confederacy as he believes that it would have been a better world if it had won the [[UsefulNotes/TheAmericanCivilWar American Civil War]].
** In "Time to Time", Lorelle Palmer has Gavin bring her to UC Berkeley on April 14, 1969 in order to prove that he is telling the truth about being a time traveler. She picked this date deliberately as it was the day that her father Tom died. She grew up believing that he was killed when the bomb that he planted in the ROTC campus headquarters detonated prematurely. However, it turns out that he had actually been attempting to deactivate the bomb when it went off. Lorelle does briefly change history and save her father but she ultimately decides to allow history to run its course after learning that the child of one of the twelve people who would have otherwise died in the explosion went on to discover a cure for AIDS. Although her father still dies, Lorelle succeeds in changing her mother Angie's life for the better. In the original timeline, Angie never recovered from Tom's death and spent most of her days in bed in Lorelle's native time of 1989. Lorelle asking her five-year-old self to tell her mother how much she loved a painting that she had made for her resulted in Angie gaining solace and comfort from pursuing art as a career.
* ''Series/WeirdScience'':
** In "By the Time We Got to Woodstock", Chett tries to prevent UsefulNotes/RichardNixon's downfall while in 1969.
** In "Camp Wannabe", Gary tries to change history by having Lisa send him back in him to Camp Wannabe in 1986 so that he can win the heart of Julia Putnam, on whom he had a crush, and spare himself the embarrassment of being tied to a tree all night by Jeremy Scanlon. He succeeds in doing so but he changes history back, albeit very reluctantly, after Julia breaks up with him and Jeremy's life is ruined.
** In "Bee In There", Gary and Wyatt ask Lisa to send them back in time in their fathers' bodies, as in ''Series/QuantumLeap'', so that they can teach their younger selves to throw a baseball and impress girls in the present. As ever, things don't go according to plan. When they arrive in 1987, Wyatt is in his father Wayne's body but Gary is in his mother Emily's body. Due to a misunderstanding involving Wyatt helping Gary take off his bra, Gary's father Al and Wyatt's mother Marcia become convinced that their spouses are having an affair. Although Gary and Wyatt are able to save their parents' marriages, they never get around to teaching the 1987 versions of themselves how to throw a ball.
* ''Series/TheTwilightZone1985'': In "Time and Teresa Golowitz", Bluestone abandons his plan to have sex with Mary Ellen Cosgrove and instead prevents the title character from [[DrivenToSuicide committing suicide]] in October 1948. In the altered history, she becomes a highly successful singer. The Prince of Darkness admits that this was his plan all along as he is a sculptor of possibilities who could not bear the idea of the world losing a talent like Teresa's at 16.
* ''Series/ElMinisterioDelTiempo'': The eponymous Ministry's ongoing job is to find the gates that open between different time periods and prevent history from changing - or restore it if someone manages to cause the change.
** Pacino kills Morán's abusive father before Morán accidentally travels forward in time to the future, where he would become a SerialKiller that Pacino's father was not able to capture - which would have led to Pacino's father's suicide.
** When a TV presenter with a bone to pick with the Ministry ends up accidentally taking UsefulNotes/ChristopherColumbus' place in history, the Ministry sends agents to capture the presenter and save Columbus from a murder attempt.
** In Season 4, Pacino tries to avert Lola's kidnapping by changing the events leading to that kidnapping. [[spoiler:They are all a failure, as the changes lead to the death of his friends, so Pacino has no choice but to let history run its course.]]
** All seasons' finales deal with this.
*** In Season 1's finale, Julián tries to save his wife from the accident that kills her. [[spoiler:Instead, his presence ends up ''causing'' the accident, as she gets distracted from seeing him in a car gets hit by another car.]]
*** In Season 2's finale, King Philip II uses the time gates to ensure that the Invincible Armada manages to take over England, but then he takes over the Ministry itself to ensure Spain's morals remain untouched. The team ends up threatening to kill Philip's younger self unless he undoes his actions.
*** In Season 3's finale, the grandson of Salvador's predecessor as Undersecretary uses his knowledge of the Ministry to unmask its secret and turn it into a business allowing people to travel in time so they can witness important events. However, this ends up causing a deadly plague to spread, particularly after the team finds a way to send it to the present time to force the man to undo his mistake. [[spoiler:It takes forcing him to travel to the future so he can see the destruction his plans will bring to the world.]]
** [[spoiler:Season 4's finale reveals the entire series was this. The ArcVillain, who managed to build a TimeMachine and took over the country, turning it into a {{Cyberpunk}} {{Dystopia}}, engineered Julián's wife's death to prevent the birth of Julián's granddaughter, who would eventually lead a resistance against the ArcVillain's rule and win. This is solved by the team finding the villain's baby self and bringing him to the present, where he is initially killed, but in a second timeline he is placed under the care of a loving family that will ensure he never goes bad.]]
* ''Series/TheUmbrellaAcademy'' is driven by this trope. In the very first episode, Number Five reveals that he has returned to 2019 in order to prevent a coming apocalypse. In season two, this is again Five's motivation, while Klaus has a plan to [[spoiler: prevent his lover Dave, who he met when he accidentally time traveled to the Vietnam War in season one, from enlisting in the army, as this will likely lead to his death]].
[[/folder]]

[[folder:Episode or Character Plots]]
* ''Series/AshVsEvilDead'': The final two episodes of Season 2 see Ash and company traveling back in time to the days just before the events of [[Film/TheEvilDead1981 the original film]], in an attempt to stop Ash's younger self from ever reading from the ''Necronomicon'', in the hopes it will prevent all the evil and tragedy that's occurred ever since, up to and including [[spoiler:Pablo's recent death]].
* In ''Series/BabylonFive'', this is a key point in the 5 year plot -- instead of "Sometimes, trying to set right what once went wrong is what [[YouAlreadyChangedThePast sets everything wrong in the first place]], resulting in a StableTimeLoop.", everything will go wrong unless the heroes go back to keep what's right, creating a StableTimeLoop by altering the past to what it is. Which gets really confusing if you try to ask, "What happened the first time?" There are a few hints via dreams and a broadcast. It's said the Shadows' army would have been three times larger and more prone to act directly earlier.
* ''Series/DoctorWho'':
** [[Recap/DoctorWhoS2E9TheTimeMeddler "The Time Meddler"]]: This how the Monk in sees his own actions: that by reversing the outcome of the Battle of Hastings, he would ensure that England gets a better king — Harold — than the one it actually got — William. The Doctor, however, is outraged by the sheer recklessness of this action.
** Not-quite-subverted in [[Recap/DoctorWhoS12E4GenesisOfTheDaleks "Genesis of the Daleks"]]. The Time Lords send the Doctor back in time to the creation of the Daleks, with the goal of either preventing their creation, or at least making them less aggressive. While there, the Doctor is captured by the Daleks' creator and is made to detail every Dalek vulnerability he knows about. Being the universe's resident expert on fighting Daleks, this would have been a catastrophe had he not [[NoPlansNoPrototypeNoBackup destroyed]] the tape before leaving the scene.
** Possibly subverted in [[Recap/DoctorWhoS21E4ResurrectionOfTheDaleks "Resurrection of the Daleks"]], where the Daleks used the Doctor's interference in their creation to justify an attack on Gallifrey.
** Creator/RussellTDavies' view was that this Dalek-Time Lord skirmishing eventually led to the Time War of the new series, thus subverting the trope. Alternatively, this could be playing the trope straight, as the Time War may actually be a ''better'' outcome than what the Time Lords originally predicted.
** This doesn't work in the Whoniverse all the time. The Series 1 episode [[Recap/DoctorWhoS27E8FathersDay "Father's Day"]] establishes that some points in time can't be changed (known as fixed points, they are usually major historical events but they could be more personal ones) without causing disaster, but other points are in flux and can be changed to varying degrees.
** [[Recap/DoctorWhoS30E11TurnLeft "Turn Left"]]: At the climax, Donna has to travel back in time to prevent a nightmarish alternate timeline from ever happening by ensuring that she makes the decision that leads to her meeting the Doctor.
** Amy gets a chance to do it in a small way in [[Recap/DoctorWhoS31E13TheBigBang "The Big Bang"]] — not by time travelling, but because [[spoiler:the universe is being rebooted from her memories, so if she remembers something the way it was, she can have it back]].
** [[Recap/DoctorWhoS32E10TheGirlWhoWaited "The Girl Who Waited"]] deconstructs this, in part. Amy gets trapped in a hospital that runs on NarniaTime, causing Rory arrive thirty-six years later, during which time she's been [[FutureBadass fighting robots]] with no living company. There's an opportunity to set things right, but Amy is not on board:
--->'''Old Amy:''' He wants to rescue Past Me from 36 years back, which means I'll [[RetGone cease to exist]]. Everything I've seen and done dissolves, time is rewritten.\\
'''Rory:''' That's ... That's good, isn't it?\\
'''Old Amy:''' I will die. Another Amy will take my place, an Amy who never got trapped at Two Streams, who grew old with you, and she, in 36 years, won't be me.
*** [[spoiler:At first, it seems she's WrongTimeTravelSavvy, but the truth is slightly more complicated, along the lines of NeverTheSelvesShallMeet.]]
** The Series 9 opening two-parter [[Recap/DoctorWhoS35E1TheMagiciansApprentice "The Magician's Apprentice"]]/[[Recap/DoctorWhoS35E2TheWitchsFamiliar "The Witch's Familiar"]] hinges on the Doctor getting a chance to fix a huge mistake he made: [[spoiler:abandoning a young, frightened Davros — who would create the Daleks as an adult — on a Skaro battlefield instead of saving his life, which likely started him on the path to evil]]. The problem is, ''how'' will the Doctor fix the mistake at a point when he has nothing to lose: [[spoiler:save him and risk the Daleks, or kill him and risk his own soul and the universe's stability]]?
*** The answer turns out to be: [[spoiler:save him, and instill in him some understanding of mercy that will eventually save Clara's life when she's trapped inside a Dalek casing by Missy in "The Witch's Familiar".]]
** [[Recap/DoctorWhoS37E3Rosa "Rosa"]]: In order to prevent the antagonist, a racist from the far future who is trying to derail the Civil Rights Movement, from succeeding, the Doctor and her friends practically have to bend over backwards to ensure that Rosa Parks is asked to give up her bus seat. Culminating in the Doctor, Graham and Yaz having to ''stay'' on the bus to ensure there are enough "white" passengers for this to happen.
* ''Series/{{Farscape}}''
** Subverted in episode "Different Destinations", where the team go back in time to a historic siege and make things ''worse'' by getting everyone except them killed.
** Played straight in "Kansas" when the team accidentally goes back to Earth in 1985 and has to prevent John's father from going on the Space Shuttle ''Challenger'' to prevent his death and John possibly never ending up on Moya.
* In an episode of ''Series/TheFlash1990'', Barry Allen is accidentally thrust 10 years into a future where Central City has been taken over by his brother's killer, Nicholas Pike, and where an underground group of citizens were waiting for [[SecondComing the Flash to return]] in order to set things right.
** The [[Series/TheFlash2014 2014 series]] takes place in a timeline caused by the Reverse Flash [[MakeWrongWhatOnceWentRight traveling back in time to Barry's childhood and killing his mother]]. In this timeline, Barry becomes the Flash several years earlier [[spoiler:thanks to the very same Reverse Flash needing Barry's access to the Speed Force]] than he was supposed to. Later, he gets several chances to fix the timeline and save his mother, [[spoiler:but ends up letting the events play out and even helps the pre-time-jump Reverse Flash get back onto the path of the new timeline]].
** Later, after Barry accidentally runs into the future, [[spoiler:and witnesses Savitar kill Iris,]] he vows to do all in his power to prevent it from occurring, while also [[ScrewDestiny deciding to live his life and be happy for long as he can. Savitar later reveals that it was Barry creating Flashpoint that gave Savitar the chance to break free of the prison Future!Barry put him in.]]
* In the second part of ''Series/TheFlipsideOfDominickHide'', "Another Flip For Dominick", Pyrus convinces himself that is what he is doing when he steps into history to foil a kidnapper. This forces Dominick to pursue him back and stop him before he completely screws things up.
* More of a case of "Set right what we messed up" but in an episode of ''Series/HannahMontana'', Miley and Jackson travel back in time and mess up their parents meeting. Cue a back to the future style disappearance for Jackson as Miley tries to set things right. It was probably AllJustADream.
* Discussed and strangely implemented in the "Time Jerker" episode of ''Series/HenryDanger''. Henry goes through a bad day where he is constantly being hurt or pranked. After a battle with the titular bad guy, Henry goes back to the morning and has to relive the same day over again. This time, he avoids all of the injuries and pranks, but messes up Jasper's model and keeps Charlotte from joining a special academic group. Ultimately, he realizes he has to go back and relive the day over again, suffering all of his ills so that his friends' accomplishments are restored.
* ''Series/KamenRiderDenO'' touches on this occasionally, in the context of "You are not supposed to do this".
** Kintaros nearly gets kicked off [=DenLiner=] in one episode when he tries to change a girls past for the better instead of dealing with the MonsterOfTheWeek (who was damaging the timeline himself in the meantime).
** Although it seems perfectly okay for them to change history in some cases but not in others. In one early episode, our heroes help a struggling musician make it to a gig which he had missed in the original timeline. He's convinced that had he not missed this gig, he'd be a star in the present. Turns out he's still a nobody even after they change history; the only difference is that he no longer blames himself for the breakup of his band. Since the change was so unimportant, our heroes are informed that what they did was okay.
** What the previous two events have in common is that the change prevented the [[MonsterOfTheWeek Imagin]] from making a DealWithTheDevil with that person in the first place. While Singularity Points negate ''some'' of the damage caused by an Imagin to the past, they only negate damage to things that were part of their memory and some things are lost for good. So completely negating the rampage ''better'' preserves the timeline than simply destroying the Imagin in the past, even if it requires a minor change. Strangely, this ''doesn't'' negate the fact the Imagin was destroyed though...
* In the NonSerialMovie of ''Series/KamenRiderKiva'', ''King of Hell Castle'', Wataru goes back in time in order to prevent a prison inmate from discovering the ruins of an ancient demon race and becoming their king. Unfortunately, his actions don't make any real difference, and in fact may have made it worse, given that when he returns to 2008, the creatures are roaming freely and the moon is covered by a gigantic monster eyeball.
* A late episode of ''Series/KaizokuSentaiGokaiger'' has Domon of the Series/MiraiSentaiTimeranger recruit the pirates to go back to 2010 to protect a shrine to obtain a Greater Power. This was used to pull an AuthorsSavingThrow concerning the team's appearance in ''Series/TensouSentaiGoseiger vs. ''[[Series/SamuraiSentaiShinkenger Shinkenger]]''. They complete the mission, but realize they didn't get the power. The shrine becomes a ChekhovsGun as it holds [[Series/NinjaSentaiKakuranger the missing Ninjaman]].
* On an episode of ''Series/KirbyBuckets'', we learn that Kirby's idol played in a band with his mother when they were in high school, but they had a very bitter falling out one day and have hated each other ever since. Kirby thus had to go back in time to stop the breakup from happening.
* Naturally, ''Series/{{Life On Mars|2006}}'' and ''Series/AshesToAshes2008'' have played with this: in Sam's case, it was finding out why his father abandoned him, as well as arresting the serial killer who'd kidnapped his girlfriend and a crime lord who'd had a witness in his custody murdered; in Alex's, it was preventing her parents' death by car bomb. Their success rates are... varied; Sam eventually wound up ''convincing'' his father to skip town, because there was that little matter of a murder and racketeering charge if he stayed...
* This is Desmond's major character motivation throughout the third season of ''Series/{{Lost}}'' (apart from his desire to be reunited with his lost love Penny).
* In the series ''Series/MirrorMirror'', there is exactly ''one'' person who was trained to do this exactly ''once'', as revealed in the final episode. Everything prior to this point had already happened in her mentor's past.
* The ''Series/MysteriousWays'' episode "Yesterday" deals with a police officer who relives the previous day after accidentally shooting and killing his partner and praying for some way to make it right.
* In the ''Series/MysteryScienceTheater3000'' episode featuring the film ''Film/TimeChasers'', Crow decides to go back in time and convinces Mike to abandon his job at a Wisconsin cheese factory and be a rock star. This causes Mike to not get sent up to the Satellite of Love as he ends up dying due to a poorly timed crowd surf attempt. In his place is his angry chain-smoking brother Eddie. Crow gets fed up with how much Eddie attacks them and goes back to stop himself from convincing Mike.
* In ''Series/TheOrville'' episode "Pria", the titular captain turns out to be a time traveler from the 29th century, who retrieves and sells unique objects, which have historically been destroyed. In this case, she saves the ''Orville'' from a NegativeSpaceWedgie, which was supposed to destroy the ship with all hands. She hijacks the ship and takes it through a wormhole into the future, but the crew manages to make it back. Ed has the wormhole destroyed, which {{Ret Gone}}s Pria, but somehow allows the ''Orville'' to survive anyway. Also used as a joke in the pilot, where Ed asks if a time-acceleration device can be used in reverse to, for example, go back a few years and prevent him from marrying his ex-wife (and XO) Kelly. [[spoiler:That ends up being the plot of the season two finale two-parter]].
* ''Series/TheOuterLimits1963'' episode "The Man Who Was Never Born". A mutant from a devastated future goes back in time to prevent the biological disaster that destroyed civilization.
* ''Series/TheOuterLimits1995'':
** In "A Stitch In Time", a scientist develops a time machine and uses it to go back and [[SerialKillerKiller kill serial killers before their first murder]]. However, it turns out she was motivated by the fact that she'd been raped and tortured by a serial killer herself as a child. She eventually goes back and kills ''him'', thus saving her younger self, but this undoes all of her other killings, as she would have had no motivation to kill them in the first place. She also dies while killing him. However, her younger self realizes that time travel is possible and uses it to re-invent the technology. In the double ClipShow "Final Appeal", she uses it to help people ([[spoiler:she dies when another time traveler blows up Washington, D.C., in the future]]).
** In "Decompression", a popular presidential candidate traveling on a plane and seeing an intangible image of a woman claiming to be from a BadFuture where his plane crashed (because of another time traveler's accidental interefence), and his ineffectual opponent ended up winning. She convinces him to jump out of the plane by claiming that she will use future technology to halt his fall moments before hitting the ground. This appears to happen, but then she explains that she is here to kill ''him'', as he is the one who will become PresidentEvil due to his paranoia. The falling scene repeats, and nobody catches him this time. The plane lands without problems. For bonus points, he's played by Bruce Boxleitner, who plays a ''good'' president in ''Series/BabylonFive''.
** In "Patient Zero", a time-traveling assassin killing certain people with a fast-acting poison before the strains of viruses they're carrying can combine in Patient Zero and start a pandemic that will kill most of humanity. Each time he goes back and is told that nothing has changed. He eventually realizes that he has to kill Patient Zero, who turns out to be a pretty woman, and he hesitates, resolving to prevent her from contacting the people with the strains. At the end of the episode, a colleague of his goes back in time and explains that the ''assassin'' is the one who is now Patient Zero, as his attempts to keep her away from the infected resulted in him creating the plague within himself. He voluntarily lets himself be poisoned in order to keep his future family safe.
** In "Breaking Point", a scientist builds a time machine and uses it to go two days into the future. There, he sees his wife dying from a gunshot wound. He goes back and desperately tries to ensure his wife's safety. Unfortunately, a side effect of time travel is his increasingly slipping sanity. In the end, he is the one who ends up shooting her two days later. In a case of WhatHaveIDone, he jumps back to the day he originally met her and kills his past self, himself erased out of existence. Unfortunately, the last shot is of the girl, who would have become his wife, clearly depressed, about to pop some pills with alcohol, possibly resulting in her death.
* ''Franchise/PowerRangers'':
** Done in ''Series/PowerRangersTurbo'', with heavily debated success. A robot, the Blue Senturion, came from a thousand years in the future to warn the heros about a war two years later... and was intercepted by the villains, who took the message, and deleted it from his memory. Not only did the war still happen, but it happened a year earlier than scheduled. On the one hand, an all-out win for Team Evil was averted, but on the other, [[Series/PowerRangersInSpace it still didn't]] [[HeroicSacrifice end very]] [[BittersweetEnding happily]].
** Another example in ''Series/PowerRangersSPD'', with [[SixthRanger the Omega Ranger]], who comes from the future to make sure the heroes win. The drawback being that he ends up being locked between his morphed form and a ball of light- Because they had no budget for a real actor.
* In ''Series/{{Primeval}}'', Matt spends the majority of season four and five doing this to prevent a BadFuture. [[spoiler:Although, as he doesn't know exactly what went wrong, and doesn't find out what went wrong until halfway through season five, he spends most of the time tracking the wrong person and helping prevent a bad present.]]
* There was an episode of ''Series/{{Roswell}}'' where a Max Evans from the future uses the Granilith to travel back to the present to break up his past self and Liz, because by staying together it results in all their deaths at the hands of their enemies, 14 years from now.
* Two episodes of ''Series/SeaQuestDSV'' involve TimeTravel and plots to fix the timeline. In the first case, the submarine is brought to a BadFuture, where a plague has wiped out most of humanity, with the rest of the people staying at home and playing video games using real HumongousMecha. By the end, only two humans are left in the world (the rest are killed by the "video games"): [[AdamAndEvePlot a boy and a girl]]. The AI controlling the world brings the ''[=seaQuest=]'' crew to the future to try to get the survivors to repopulate the species. However, to do that, they need to [[spoiler:remove their dependence on the very same AI by shutting it off permanently]]. As [[TeenGenius Lucas]] [[TimeyWimeyBall tries to explain]], the way time works is that the future and the past are in a StableTimeLoop of sorts, and, by saving the future, they're ensuring their own past.
** The second example has a reactor instability result in a [[NegativeSpaceWedgie Negative Sea Wedgie]] sending the sub into the middle of the [[UsefulNotes/HistoryOfTheColdWar Cuban Missile Crisis]]. Or, rather, the first time jump has the sub arrive days after the crisis goes apeship, and the superpowers nuke the world. They find a lone yacht at sea with a naval officer dying from radiation explaining what went wrong during the crisis. The sub then jumps back a few days and tries to ensure that events are put back on course as they remember from their history lessons. Specifically, an American sub ends up being out of position and assumes that a Soviet ship has already crossed the line, when, in fact, it's miles away from it. The attack on the ship would've started WorldWarThree. The ''[=seaQuest=]'' manages to intercept the torpedo and uses the command codes provided by the same officer to order the US sub back in position.
* ''Series/StargateSG1''
** Subverted in "The Gamekeeper": Jack and Daniel ''think'' that they're being sent to the past to fix mistakes in their lives, but it turns out that they're just mentally reliving them, not really time travelling, and there's no way for them to fix it anyways.
** Played straight in the Aschen arc, in the episodes "2010" and "2001". The former takes place in a BadFuture, where the Aschen, posing as benevolent aliens, infect Earth with a sterility vaccine that will eventually cause its population to die out. To avert it, SG-1 sends a [[NoteToSelf note to their past selves]] back in time, leading to a less tragic future.
** Played straight in the two-parter "Moebius" when an attempt to go back in time to retrieve a piece of technology results in screwing up the timeline and having to go back in time again to fix it.
** Also played straight in the movie ''Continuum'' as listed in the "Films" section.
* The ''Series/StargateAtlantis'' episode "The Last Man" has Sheppard thrown 48,000 years into the future, where a program Rodney left behind recounts a long FromBadToWorse story of the intervening years and arranges to send Sheppard back to fix everything. He even gives Sheppard some crucial information, like Teyla's location at the time, so Sheppard can change what happened for the better.
* ''Series/StargateUniverse'' has a particularly complex example in "Time". The episode initially plays like FoundFootageFilms, as scene as recordings on a kino. It then becomes apparent the crew of ''Destiny'' found a kino that had been sent back in time on alien planet. The footage shows how the team was slaughtered by the local predators; but ''also'' reveals they (and as such the current ''Destiny'' crew as well) all have a fatal virus from tainted water, and the predator venom acts as cure. [[spoiler:In a rather brilliant twist, the first attempt to fix things ends in disaster with more deaths. The episode ends with Scott throwing another kino back in time, leaving a different version of ''Destiny'' to get it right.]]
* Guinan of ''Series/StarTrekTheNextGeneration'' is practically this trope walking personified (as for reasons that were never even hinted at until TheMovie, changes in the timeline do not affect her), especially in "Yesterday's Enterprise". More technically they don't entirely affect her. She could identify something was wrong, but didn't know what could have caused it.
** In "Tapestry", Q gives Picard the opportunity to avoid a BarBrawl in which he suffered a near-fatal wound to his heart, leading to getting an artificial heart that failed him in the beginning of the episode. [[ForWantOfANail Picard however finds that not being in the brawl drastically changed his future, as he's not a legendary captain, but a lowly lieutenant.]]
* The iconic ''[[Series/StarTrekTheOriginalSeries TOS]]'' episode "The City on the Edge of Forever": We see what's happened when [=McCoy=] goes through the Guardian: Edith Keeler starts a revolution, causing the Germans to win WWII, causing havoc and destruction throughout the timeline. Kirk and Spock must enter and make sure Keeler dies like she's supposed to. Of course, a little thing called love gets in the way...
* The conclusion of the ''Series/StarTrekVoyager'' "Year of Hell" serial. Or for that matter, the conclusion to the series altogether.
* In the Season One finale of ''Series/StarTrekStrangeNewWorlds'', "A Quality of Mercy", [[spoiler:Pike attempts to ScrewDestiny by writing and convincing the future cadets to not be there the day he is meant to be hideously disfigured saving them. He is confronted by an alternate future ''Admiral'' Pike, who shows him that doing so will lead to a reignition of the Federation-Romulan War.]]
* ''Series/{{Supernatural}}'': Plays with this trope but never quite plays it straight.
** In Season 2, A djinn grants Dean a wish and he wakes up in an alternate universe in which his mother never died and he and Sam never became hunters. Sam is happy but estranged from Dean who lives an ordinary life as a mechanic with a drinking problem. When Dean realizes that all the people that John, Sam, and Dean saved are dead, he sets out to restore the timeline by hunting the djinn. [[spoiler: It turns out he's in a MentalWorld created by the djinn not in an actual alternate timeline.]]
** In "In The Beginning", Dean ''thinks'' that his jump into the past is to set right what once went wrong (Castiel all but states it outright), but not only does it turn out he was only meant to ''witness'' what went wrong and not change it, it sure looks like he actually ''caused'' it. Castiel eventually makes it clear that it was a closed time loop and Dean can't fight fate.
** In "The End" Zachariah sends Dean to a BadFuture where Dean is a hardened guerrilla, Cas is a drug-addled sex guru and Sam has [[spoiler: said yes to Lucifer.]] Zachariah is trying to convince Dean to say yes to Michael, but Dean instead resolves to end his estrangement with Sam.
** "The Song Remains The Same" had an angel go back to that time to try to kill Sam and Dean's mother before they were born in order to stop the Apocalypse. While she seemingly succeeds in killing their father, he is brought back as a vessel for Archangel Michael, who kills the angel.
** {{Inverted}} in "My Heart Will Go On" the brothers find themselves in an alternate timeline where the ''Titanic'' never sank, Jo and Ellen are alive and Ellen is happily married to Bobby. Also, Music/CelineDion is a broke lounge singer and the boys drive a Mustang. It's arguably a better timeline than [[CrapsackWorld their own]] but it enrages the fates so the timeline must be set right.
** In "As Time Goes By", Henry wants to return to 1958 to stop Abaddon and be a father to John, but Dean fears that it'll have an unforeseen consequence and stops him by force. Although even Dean is taken aback when Henry points out that his return would mean that the Apocalypse and all the other [[SealedEvilInACan sealed evils]] that have killed thousands of people would never have been released.
* ''Series/VanHelsing2016'': The first three episodes of Season 5 see Vanessa sending Jack back in time to medieval Transylvania in order to prevent the original rise of [[MonsterProgenitor the Dark One]]. [[spoiler: She manages to change some details, but ultimately fails to change the final outcome.]]
* ''Series/TheXFiles'' episode "Synchrony" presents the case of a strange old man warning an MIT student and professor that the student is going to die at a specific time -- because of this warning the professor, attempting to save the student, ends up accidentally pushing him into the path of an oncoming bus and thus the warning is a SelfFulfillingProphecy. The old man is [[spoiler:actually the professor from the future, who has traveled back in time]] attempting to Set Right What Will Go Wrong and prevent an impending scientific breakthrough [[spoiler:that would be made by the professor in collaboration with his girlfriend, also a scientist, and the student, and which would be a catalyst for a catastrophic technological development.]] Mulder cites an old theory of Scully's about how YouCantFightFate, and so the old man's efforts are probably doomed. [[spoiler:Although the professor manages to kill both his present and future selves and erase all of his files, as the episode ends, the girlfriend is continuing the research on her own with backups of the erased data.]]
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[[SetRightWhatOnceWentWrong Setting Right What Once Went Wrong]] in LiveActionTV
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