History Main / RetroactivePreparation

* In ''The Overlords of War'' by Gerard Klein, the main characters need to depose an alien dynasty distinguished by laying blue eggs. They travel to the past when the current ruler had just hatched, replace the shards of his egg with another, but painted, and then, in the present, expose it as a fake, making him appear illegitimate.

%%* Creator/JackMcDevitt's novel ''Time Travelers Never Die'' makes extensive use of this principle.

->''"This always made much more sense to me -- that there would be a spark at some point along the loop, some sort of injection of energy or effort of will which kicked it all off, someone who decided one day: "What's needed here is a causal loop.""''

[[quoteright:350:[[Webcomic/IrregularWebcomic https://static.tvtropes.org/pmwiki/pub/images/timetravel.png]]]]
[[caption-width-right:350:I must remember to add an image here in the future...]]

%% Administrivia/ZeroContextExample entries are not allowed on wiki pages. All such entries have been commented out. Add context to the entries before uncommenting them.

->''"This always made much more sense to me - that there would be a spark at some point along the loop, some sort of injection of energy or effort of will which kicked it all off, someone who decided one day: "What's needed here is a causal loop.""''

[[folder:Anime and Manga]]
* In ''[[Literature/HaruhiSuzumiya The Disappearance of Haruhi Suzumiya]]'', Kyon [[spoiler: mobilizes the SOS-dan to come back in time and save himself from Asakura and fix the whole parallel universe thing.]]
[[/folder]]

* A variation occurs in ''[[ComicBook/SupermanAndBatmanGenerations Superman and Batman Generations III]]'': [[spoiler:{{ComicBook/Darkseid}}'s plan to conquer Earth starts by sending an invasion fleet to attack the planet. Should they fail, the survivors time travel back 100 years and try again, and so on and so forth.]]
* Loki in ''Comicbook/LokiAgentOfAsgard'' went back in time (or maybe in [[TheoryOfNarrativeCausality story]]) to create the sword that was used to free [[spoiler:Thor]] from their parasitic influence, because they wanted to wreak havoc without the restrictions of, well, basically DemonicPossession. In this case the time loop wasn't as stable as expected though so it invited the ButterflyOfDoom over unintentionally creating [[OnlyFriend Verity Willis]].
* ''ComicBook/TerminatorRoboCopKillHuman'' features a variation. [=RoboCop=] uses time travel to give a young Dick Jones the schematics for the ED-209, (thus ensuring that OCP will become the MegaCorp it is destined to become), with his only condition being that Jones and a squad of 209s show up at a VERY specific place and time in the "future" (ie the comic's present) to assist in the final battle.

[[folder:Fanfiction]]

* In ''Fanfic/KyonBigDamnHero'', Kyon has to travel several days back to prepare countermeasures when [[spoiler:Sasaki is kidnapped]].
** At one point the SOS Brigade is in an urgent need of a dimensional anchor. Immediately after Kyon realizes one may be in Tsuruya's possession there's a knock on the door: Tsuruya just arrived to the clubroom to deliver the dimensional anchor, as per requested by Kyon('s future self).
%%* ''FanFic/HarryPotterAndTheMethodsOfRationality'' plays {{Xanatos Speed Chess}} with this trope.

[[folder:Films — Live-Action]]
* Not only is it used in ''Film/BillAndTedsExcellentAdventure'', it's practically elevated to a martial art in ''Film/BillAndTedsBogusJourney'', where the climax has both the titular heroes and their nemesis making use of this trope [[spoiler: before pointing out that only the ''winner'' of the showdown can actually make use of it]].
* In ''Film/{{Tenet}}'', this happens during the FinalBattle. The Protagonist and Ives arrive at the cave, but there's a locked door between them and Sator's right-hand man Volkov, who is [[spoiler:burying the Algorithm for the people from the future to find. Fortunately, an inverted corpse springs back to life, takes a bullet meant for The Protagonist, and opens the door, allowing The Protagonist and Ives to overpower Volkov and retrieve the Algorithm. When the battle is over, it's implied Neil will eventually invert so he can open the door and [[HeroicSacrifice take the bullet]]]].

* This is the premise of Creator/PhilipKDick's short story "Paycheck".
* Creator/JackMcDevitt's novel ''Time Travelers Never Die'' makes extensive use of this principle.
* So does ''Literature/TheManWhoFoldedHimself'' by David Gerrold, the time traveler using it even to get "immortal".
* {{Subverted|Trope}} in ''Literature/TheRiftwarCycle'' where Pug sometimes receive instructions apparently written by himself in the future. They are actually written by the god Kalkin.
* We will never know for sure, but this appears to be what's going on in the surviving fragment of ''Literature/TheSalmonOfDoubt'', with a number of things making a lot more sense if you assume [[spoiler: that a Dirk Gently from the future is making sure present Dirk ends up in the right place]].

* In ''The Overlords Of War'' by Gerard Klein, the main characters need to depose an alien dynasty distinguished by laying blue eggs. They travel to the past when the current ruler had just hatched, replace the shards of his egg with another, but painted, and then, in the present, expose it as a fake, making him appear illegitimate.

[[folder:Live Action TV]]

** The Seventh Doctor became particularly associated with this, mostly due to [[Recap/DoctorWhoS26E1Battlefield "Battlefield"]], in which he finds himself resolving an issue created by a future incarnation, and [[Recap/DoctorWhoS26E3TheCurseOfFenric "The Curse of Fenric"]], in which he's been fighting Fenric on multiple levels in different time periods. By the time of the ''Literature/DoctorWhoNewAdventures'', it had become memetic that he ''always'' did this, so the books started playing with it (see above).
** Parodied in the non-canonical ''[[Recap/DoctorWhoTheCurseOfFatalDeath The Curse of Fatal Death]]'', where both the Doctor and the Master attempt this, repeatedly going back in time to bribe the architect of the castle they're in to plant a series of traps to be used against the other.
** This is the Doctor's only recourse in [[Recap/DoctorWhoS29E10Blink "Blink"]], not so much helping himself as helping Sally Sparrow defeat the Weeping Angels in 2007 because they sent him back to 1969 without the TARDIS.
** Because of this rule, the Doctor was able to save River Song in [[Recap/DoctorWhoS30E9ForestOfTheDead "Forest of the Dead"]], as he realised that, knowing about her death, he now had plenty of time to find a way to save her.
** Used in the Series 5 finale [[Recap/DoctorWhoS31E13TheBigBang "The Big Bang"]], repeatedly, where we first see the Doctor show up and give random orders, leave, come back a second later, give more, and repeat a few times. Later, we see it from the other side, and learn he's doing this in real time in the future as he figures out what he needed to have already have happened. Thanks to the TimeyWimeyBall in that universe, he probably can't rely on things he's going to do later, so going back and retroactively doing them the instant before he needs them is safer.
*** Rather cleverly at the very end, we find out that two events earlier in the series that didn't make much sense at the time (the TARDIS returning to young Amy waiting on the Doctor, despite us knowing that she didn't see him again till twelve years later; and the Doctor telling Amy to 'remember what I told you when you were seven') turn out to be future versions of the Doctor, setting things up so Amy will remember him. [[spoiler:Well, actually, it's the Doctor reversing through his own timeline as he gets erased from time, so he's really just taking advantage of involuntary time travel rather than having planned it, but it works the same way]].
** Straight-up depended upon by the Doctor in [[Recap/DoctorWho2011RNDSSpaceAndTime the Red Nose Day special "Time"]]:

'''Future Doctor:''' The [[InherentlyFunnyWords wibbly]] [[TechnoBabble lever]]!
** Taken to ridiculous levels in [[Recap/DoctorWho50thASTheDayOfTheDoctor "The Day of the Doctor"]], where the Doctor pulls off a thousand-year preparation in order to [[spoiler:save Gallifrey by placing it in a time lock]].
** Taken advantage of by Missy in [[Recap/DoctorWhoS36E12TheDoctorFalls "The Doctor Falls"]]. When her [[TheNthDoctor previous incarnation]] reveals that his/their TARDIS is inoperable due to a broken piece of [[AppliedPhlebotinum Phlebotinum]], she invokes this trope. She throws said previous incarnation against the wall, and claims that she "remembers" a very scary lady once throwing her against the wall and forced her/him to promise to always carry a spare piece of that phlebotinum at all times. The promise made, she then reaches into her own pocket to reveal that she now has the exact piece of phlebotinum they need.
** [[Recap/DoctorWhoS38E1E2Spyfall "Spyfall"]]: The Thirteenth Doctor uses this to save her companions' lives when [[spoiler:they're left on a crashing, cockpit-less plane by the Master in the first half's {{cliffhanger}}. After being reminded to do so near the end of the story, the Doctor travels back in time to the construction of the plane to plant notes and features so Ryan knows to plug his phone into the plane's computers to control it.]]

* Averted in ''Series/SevenDays'', when the Russians manage to get their time travel technology off the ground thanks to Olga. Unfortunately, the technology is controlled by a rogue Russian general who proceeds to kill the Russian president and take power, intending to use the Sphere to prevent any attempts to remove him from power. Parker manages to "backstep" and stop the Russian program before their first jump. Interestingly, Olga previously worked on another Russian time travel program, which did not bear fruit but got her recruited into the Backstep program.
* ''Series/StargateSG1'' two-part episode "Moebius" may not be a straight example, but it probably felt like that to the characters. In the beginning, they need a Zero-Point Module, decide to go back in time to when there was one on Earth, then hide it in a recently-discovered excavation site. At the end, General O'Neill finds himself watching a video of himself and his team explaining how and why they went back in time, which was recently discovered at an excavation site alongside the Zero-Point Module they needed. The only part O'Neill understands is that he doesn't have to do anything now that someone from another timeline did it for him.
-->'''Jack O'Neill:''' So... we don't have to go back in time and get the ZPM because... we already went back in time and got the ZPM?\\
'''Sam Carter:''' ... Pretty much.\\
'''Jack O'Neill:''' ... Alright then, let's go fishing.

* In the time-traveling RPG ''TabletopGame/{{Continuum}}'', this is called "slipshanking," and it's a viable alternative to [[HelpYourselfInTheFuture your future self actually showing]] up to help you out of a jam (a "Gemini"). Contrary to the Bill & Ted example, an immediate frag penalty is assessed which can only be resolved by somebody (usually yourself) travelling back in time, obtaining the object elsewhere (NOT the one that was just given to you), and placing it for you to find. Too much slipshanking is a sign of poor planning, and a rude imposition on your future self who has other things to do. Narcissists, of course, don't care for their future selves, and will thus do this much more often.
* This is one of the bonus options in ''[[http://dig1000holes.wordpress.com/time-temp/ Time and Temp]]'' after you've gathered enough knowledge to come up with a good plan (represented by writing your die rolls into a grid and creating certain patterns).

* ''VideoGame/TimeSplittersFuturePerfect'' had numerous examples of this. One of the earliest examples is also one of the most memorable - you are given a key by your future self that you need to progress, and later pass the key on to your past self, [[TemporalParadox leaving its initial existence unexplained]]. FridgeLogic also sets in when you consider the fact that ''one'' key is being infinitely passed from Cortez to Cortez, meaning it'll probably wear down and break at some point.
* In ''VideoGame/{{Achron}}'' this is a very basic tactic. If your base is attacked, you can go back and build defenses in preparation.

* The ''Franchise/KingdomHearts'' series is the result of the BigBad Xehanort doing this to himself. He uses his past self in his schemes to get the X-Blade, thus planting a seed of darkness in his past self's heart, which acts as a catalyst to eventually corrupt him into the monster that he becomes, [[StableTimeLoop who eventually uses his past self in his schemes...]]
* ''VideoGame/CallOfDutyZombies'' has a doozy, which doubles as a StableTimeLoop. The crew of Dempsey, Takeo, Nikolai and Richtofen save a girl stuck in an alternate dimension using ancient replicas of magical staffs in 1917. Over the course of several years they then endeavor to save their own souls as child-versions for a world free of evil. This pure world is then infested with evil, which the heroes then defeat; [[spoiler:only for the deity of the world to attempt to erase them from existence, before dumping them in a 'corner of time alongside some other random stuff'. Said point in time ends up being the war where they build magical staffs to fend off the evil, thus creating the very moment that they were drawn to in the first place.]] Since the staffs were explicitly ''replicas'' modelled after the originals, they knew [[spoiler:they needed to make the originals themselves.]]
* In ''VideoGame/NeverwinterNights'', you need to fight some nearly invincible golems at one point. You can travel to the past and convince the slaves working on them to introduce vulnerability to a certain type of damage.

* Thomas Overbeck's ''Webcomic/TimesLikeThis'', a webcomic focused on time travel, makes an art out of this.
* ''{{Webcomic/Homestuck}}'': {{Stable Time Loop}}s are everywhere in this series, and there are devices that can send anything to any point in time as well as devices that can pull anything from any point in time as long as no paradoxes are created. The best example is the Bunny - [[ZigZaggedTrope although it also helps cause the problems it was created to solve]].
** Dave, the Knight of Time, has this as his modus operandi, using time duplicates to aid him in everything from combat to stock trading scams. As time travel in Homestuck is semi-deterministic (you CAN change the timeline and create a paradox, but doing so causes you to branch off into a doomed timeline where everyone dies), Dave has to be very careful that he does everything that he's "supposed to do" after he's seen his future self do it. The question of where his future selves' actions originate in the first place is brought up, and he admits that he operates mainly on instinct and tries not to think about it too hard. Eventually he decides the pressure of keeping all his loops stable is too much and decides to lay off time travel for good.
** A more subtle example: The trolls have the ability to contact anyone at any point in their timeline - up until a TimeCrash event. That TimeCrash event turns out to be important, so they eventually help the human characters create the event by telling them what they do in the future and passing on information from their future selves. This eventually leads the humans to do those things and pass on that information to the trolls.

[[folder:Web Original]]
* The OldeEnglish sketch "Pizza Delivery" parodies this in a RunningGag whereby all the preparation is for the sake of, well, pizza delivery.

%%* This trope sets the plot in motion in the ''WesternAnimation/{{Futurama}}'' movie ''Bender's Big Score''.
* In the ''WesternAnimation/KimPossible'' movie "A Sitch in Time", [[spoiler:Shego]] used the time monkey idol to change a whole lot of things, including making tons of money by buying a big company before the bubble burst, [[TimeyWimeyBall causing Ron to move to Norway]], [[TakeOverTheWorld Taking Over The World]] by mind probing the entire population, [[TimeyWimeyBall and travelling back to the future!past to tell her past self to steal the Time Monkey Idol]].
* The ''WesternAnimation/RickAndMorty'' episode "Rattlestar Ricklactica" has Rick be obviously smart enough to use this method when he is dragged into TimeTravel shenanigans, but it turns into an effective but needlessly unpleasant execution of the trope due to his abrasive self-sabotaging personality and irritation with Morty. After Morty inadvertently alters the course of evolution for a planet of sapient snakes, whose warring future factions send a TerminatorTwosome after the family, Rick's plan to put a stop to the whole thing on Snake World encounters a snag as he's confronted with a problem that will take several hours to solve, so he makes a mental note to "commit even more to [Morty's] f**kup". Seconds later, a second Rick and Morty walk into the room carrying the supplies needed for the next stage of Rick's plan. The future Rick and Morty are extremely rude to their counterparts as they hand things over, and future Morty sports a black eye. It turns out that while their preparation helped them then and there, they wind up having to put off celebrating Christmas later on to put things together, basically for no reason except to fulfill the StableTimeLoop where Rick winds up being the cause of Morty's black eye a few hours later.

** Xanatos went back in the past, contacting a long lasting secret society, giving them some coins from this time as well as a letter, with explicit instructions to give himself the coins/letter in the future. The coins (as well as instructions how to best use the wealth from it) form the basis of Xanatos' massive wealth. The letter also includes instructions on how to travel back in time to give himself the new letter. Also it is implied that part of this scheme exists just so Xanatos can tell his father that he is technically a "self made man."
** A wizard uses the same time travel device to basically turn himself into a God. He uses time travel to save himself from death, gives his past self allies, massive amounts of magical power, teaches himself everything he needs to know, then sends the newly empowered self back in time to redo the process.

* In the time-traveling RPG ''TabletopGame/{{Continuum}}'', this is called "slipshanking," and it's a viable alternative to [[HelpYourselfInTheFuture your future self actually showing]] up to help you out of a jam (a "Gemini"). Contrary to the Bill & Ted example, an immediate frag penalty is assessed which can only be resolved by somebody (usually yourself) travelling back in time, obtaining the object elsewhere, and placing it for you to find. Too much slipshanking is a sign of poor planning, and a rude imposition on your future self who has other things to do.

* In ''[[LightNovel/HaruhiSuzumiya The Disappearance of Haruhi Suzumiya]]'', Kyon [[spoiler: mobilizes the SOS-dan to come back in time and save himself from Asakura and fix the whole parallel universe thing.]]

** Straight-up depended upon by the Doctor in [[Recap/DoctorWho2011RedNoseDaySpecialSpaceAndTime the Red Nose Day special "Time"]]:

* ''VideoGame/NaziZombies'' has a doozy, which doubles as a StableTimeLoop. The crew of Dempsey, Takeo, Nikolai and Richtofen save a girl stuck in an alternate dimension using ancient replicas of magical staffs in 1917. Over the course of several years they then endeavor to save their own souls as child-versions for a world free of evil. This pure world is then infested with evil, which the heroes then defeat; [[spoiler:only for the deity of the world to attempt to erase them from existence, before dumping them in a 'corner of time alongside some other random stuff'. Said point in time ends up being the war where they build magical staffs to fend off the evil, thus creating the very moment that they were drawn to in the first place.]] Since the staffs were explicitly ''replicas'' modelled after the originals, they knew [[spoiler:they needed to make the originals themselves.]]

* ''VideoGame/NaziZombies'' has a doozy, which doubles as a StableTimeLoop. The crew of Dempsey, Takeo, Nikolai and Richtofen save a girl stuck in an alternate dimension using ancient replicas of magical staffs in 1917. Over the course of several years they then endeavor to save their own souls as child-versions for a world free of evil. This pure world is then infested with evil, which the heroes then defeat; [[spoiler:only for the deity of the world to attempt to erase them from existance, before dumping them in a 'corner of time alongside some other random stuff'. Said point in time ends up being the war where they build magical staffs to fend off the evil, thus creating the very moment that they were drawn to in the first place.]] Since the staffs were explicitly ''replicas'' modelled after the originals, they knew [[spoiler:they needed to make the originals themselves.]]

* In ''Film/{{Paycheck}}'', Ben Affleck's character does this not by going back in time, but by seeing the future before his memory is wiped and planting various clues to lead him on the path that will allow him to destroy his creation.

* A card in ''TabletopGame/{{Chrononauts}}'' is called "Memo from Your Future Self". it effectively works like this, instantly negating the last card another player played. The German Chocolate Cake artifact can also be used as a Memo and the image on the card shows it having a postcard attached. (WordOfGod [[http://www.wunderland.com/LooneyLabs/Chrononauts/Mysteries.html#1.1 says]] that it is not the postcard but the cake itself, and that the cake is just so good that it distracts the other player from [[TimeTravelTenseTrouble doing what they just did]]. Presumably the postcard is just to tell yourself when to use it.)

* [[spoiler:Old!]]Loki in ''Comicbook/LokiAgentOfAsgard'' went back in time (or maybe in [[TheoryOfNarrativeCausality story]]) to create the sword that was used to free [[spoiler:Thor]] from their parasitic influence, because they wanted to wreak havoc without the restrictions of, well, basically DemonicPossession. In this case the time loop wasn't as stable as expected though so it invited the ButterflyOfDoom over unintentionally creating [[OnlyFriend Verity Willis]].

* A card in ''TabletopGame/{{Chrononauts}}'' is called "Memo from Your Future Self". it effectively works like this, instantly negating the last card another player played. The German Chocolate Cake artifact can also be used as a Memo and the image on the card shows it having a postcard attached. (WordofGod [[http://www.wunderland.com/LooneyLabs/Chrononauts/Mysteries.html#1.1 says]] that it is not the postcard but the cake itself, and that the cake is just so good that it distracts the other player from [[TimeTravelTenseTrouble doing what they just did]]. Presumably the postcard is just to tell yourself when to use it.)

->''"This always made much more sense to me - that there would be a spark at some point along the loop, some sort of injection of energy or effort of will which kicked it all off, someone who decided one day: "What's needed here is a [[StableTimeLoop causal loop]].""''
-->-- '''Website/ThingsOfInterest''', discussing how time travel works in Film/BillAndTedsExcellentAdventure

Let's say your favorite show is about to air, but you forgot to program your [[TechnologyMarchesOn VCR or DVR]] to record it. You run up to your front door to set that up, discover it locked, and realize you don't have your keys. What do you do? Break a window? Bust down the door? Drop down the chimney? Watch it at a neighbor's house? Hurry! There's less than a minute left! Oh, if only you'd thought to leave a KeyUnderTheDoormat or something!

* In the time-traveling RPG ''TabletopGame/{{Continuum}}'', this is called "slipshanking," and it's a viable alternative to [[HelpYourselfInTheFuture your future self actually showing]] up to help you out of a jam (a "Gemini"). Contrary to the Bill & Ted example, the game's rules insist that the player arrange the slipshank in-game, or take a Frag penalty. Too much slipshanking is a sign of poor planning, and a rude imposition on your future self who has other things to do.

* Used a twice in ''WesternAnimation/{{Gargoyles}}'' (which runs on strict StableTimeLoop logic) by characters to give themselves extreme wealth/power.

** A wizard uses the same time travel device to basically turn himself into a God. He uses the time travel to save himself from death, gives his past self allies, massive amounts of magical power, teaches himself everything he needs to know, then sends the newly empowered self back in time to redo the process.

* Used a twice in ''WesternAnimation/Gargoyles'' (which runs on strict StableTimeLoop logic) by characters to give themselves extreme wealth/power.

A TimeTravel trope, Retroactive Preparation is a twist on the YouAlreadyChangedThePast plot where the existence of a StableTimeLoop works to the advantage of the character's goals rather than thwarting them.

* ''Anime/PuellaMagiMadokaMagica'' has [[spoiler: Homura]], who combines her [[ResetButton time]] [[GroundhogDayLoop powers]] to try and [[spoiler: save Madoka]]. At this point, she's basically running a NewGamePlus with all the [[HyperspaceArsenal weapons]] and experience she's gained.

* In ''Film/{{Paycheck}}'', Ben Affleck's character does this not by going back in time, but by seeing the future before being stricken with amnesia.

** Parodied in the non-canonical ''[[Recap/DoctorWhoTheCurseOfFatalDeath The Curse of Fatal Death]]'', where both the Doctor and the Master attempt this. Repeatedly.

** Because of this rule, the Doctor was able to save River Song in [[Recap/DoctorWhoS30E9ForestOfTheDead "Forest of the Dead"]].

*** Rather cleverly at the very end, we find out that two events earlier in the series that didn't make much sense at the time (the TARDIS returning to young Amy waiting on the Doctor, despite us knowing that she didn't see him again till twelve years later; and the Doctor telling Amy to 'remember what I told you when you were seven') turn out to be future versions of the Doctor, setting things up so Amy will remember him. [[spoiler:Well, actually, it's the Doctor reversing through his own timeline as he gets erased from time, so he's really just taking advantage of involuntary time travel rather than having planned it, but it works the same way.]]

** The movie ''[[Film/StargateContinuum Continuum]]'' brings up the question: what if both sides have time travel technology? Ba'al attempts to use this rule, but is defeated when Mitchell travels back even further and stops him in the past. Confused yet?

* In ''Literature/ArtemisFowl: The Time Paradox'', Artemis and Holly use this once to get out of trouble, but a second attempt falls flat.

[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/timetravel.png]]

* The ''WesternAnimation/RickAndMorty'' episode "Rattlestar Ricklactica" has Rick use this method when he is dragged into TimeTravel shenanigans, although Rick's abrasive personality and irritation with Morty makes it a somewhat unpleasant overall experience. After Morty inadvertently alters the course of evolution for a planet of sapient snakes, whose warring future factions send a TerminatorTwosome after the family, Rick's plan to put a stop to things encounters a snag as he's confronted with a problem that will take several hours to solve, so he makes a mental note to "commit even more to [Morty's] f**kup". Seconds later, a second Rick and Morty walk into the room carrying the supplies needed for the next stage of Rick's plan. The future Rick and Morty are extremely rude to their counterparts as they hand things over, and future Morty sports a black eye. It turns out that while their preparation helped them then and there, they wind up having to put off celebrating Christmas later on to put things together, basically for no reason except to fulfill the StableTimeLoop where Rick winds up being the cause of Morty's black eye a few hours later.