History Main / InnocuouslyImportantEpisode

* ''Franchise/HarryPotter'':
** ''Literature/HarryPotterAndTheChamberOfSecrets'' set up ''Literature/HarryPotterAndTheHalfBloodPrince'' seven years in advance. It set up the concepts of Horcruxes through [[spoiler:Riddle's diary]], it introduced the four Hogwarts founders and established Voldemort's connection to the Slytherin bloodline, the basilisk fang from the Chamber would later be used [[spoiler:to destroy two of the Horcruxes]], and the idea that Voldemort inadvertently passed some of his abilities to Harry would prove to be ''major'' {{foreshadowing}} for the revelation that [[spoiler:Harry was an accidental Horcrux]]. It introduced Ron's sister Ginny (who would become Harry's primary love interest by ''Half-Blood Prince''), and the concept of [[FantasticRacism "blood purity" and Pureblood supremacy]] would become major lynchpins of the mythos by the end. And in one scene, Nearly Headless Nick convinces Peeves to destroy a cabinet to distract Filch for Harry; the broken cabinet becomes a major plot point in ''Half-Blood Prince''. Not bad for a work that at first glance looks like a book-long WackyWaysideTribe.

** ''Literature/HarryPotterAndTheChamberOfSecrets'' set up ''Literature/HarryPotterAndTheHalfBloodPrince'' seven years in advance. It set up the concepts of Horcruxes through [[spoiler: Riddle's diary]], it introduced the four Hogwarts founders and established Voldemort's connection to the Slytherin bloodline, the basilisk fang from the Chamber would later be used [[spoiler: to destroy two of the Horcruxes]], and the idea that Voldemort inadvertently passed some of his abilities to Harry would prove to be ''major'' {{foreshadowing}} for the revelation that [[spoiler: Harry was an accidental Horcrux]]. It introduced Ron's sister Ginny (who would become Harry's primary love interest by ''Half-Blood Prince''), and the concept of [[FantasticRacism "blood purity" and Pureblood supremacy]] would become major lynchpins of the mythos by the end. And in one scene, Nearly Headless Nick convinces Peeves to destroy a cabinet to distract Filch for Harry; the broken cabinet becomes a major plot point in ''Half-Blood Prince''. Not bad for a work that at first glance looks like a book-long WackyWaysideTribe.
* ''Literature/TheHitchhikersGuideToTheGalaxyTrilogy'' sets up a few of them, mostly in [[Literature/TheHitchhikersGuideToTheGalaxy1 the first book]]. A person is mentioned in the prologue and then dismissed with "but this is not her story"; the same prologue is used in [[Literature/SoLongAndThanksForAllTheFish the fourth book]], only now it ''is'' her story (as well as Arthur's). Then there's Arthur's first encounter with Vogons, in which he says [[spoiler:that he wished he had a daughter so he could forbid her to marry one. [[Literature/MostlyHarmless Four books later]], he ''does'' have a daughter, and she's quite rebellious--though she and the sympathetic Vogon character introduced in the sixth book never actually meet]]. Finally, there's that bit about the bowl of petunias thinking "Oh no, not again", and the book says that if we knew why it was thinking that, we might know a lot more about the universe than we do now. We find out the answer in [[Literature/LifeTheUniverseAndEverything the third book]]. Notably, Douglas Adams was making it up as he went along, and would deliberately leave threads like these dangling with no idea of what, if anything, he was going to do with them. So when he did tie up a loose end, it was as much a surprise to him as to the rest of us. Another example is the implication from Arthur's encounter with Agrajag in ''Life, The Universe and Everything'' that [[spoiler:Arthur cannot die until he's been to Stavromula Beta]], which doesn't even seem to occur to Adams until two books later, when he has to construct a kind of ShaggyDogStory (and an incredibly lame pun) to wrap up a loose end he hadn't even acknowledged previously.

* ''Literature/BridgeOfBirds'': Every seeming WackyWaysideTribe turns out to be this by the end.

An episode or installment that seems to have [[{{Filler}} little importance]] to the main StoryArc-- until [[TheReveal a major revelation]] turns out to have great significance. Basically, it's a WhamEpisode that hides its nature as one from the audience at first. It could be that TheStinger reveals the GreaterScopeVillain was [[TheManBehindTheMan involved behind the scenes]], or that a random trinket the hero picks up turns out six months later is what can unlock the SealedEvilInACan.

** The 9th issue of [[ComicBook/ActionComicsNew52 Grant Morrison's run]] on ''ComicBook/ActionComics'', sandwiched between "Superman Versus Brainiac, Fuck Yeah" and "Superman Versus Captain Comet (While ComicBook/{{Batman}} Chuckles At His Secret Identity Problems)" was an interlude involving parallel universes, a CorruptCorporateExecutive who creates a machine of incredible power allowing a monster to enter his world, and a black version of Superman who is the president of his America. [[spoiler:The monster, Superdoom, comes to fight the main universe Superman in issues 17 and 18. It also turns out that the machine's creation is the result of events in ''ComicBook/TheMultiversity''.]]

** ''Film/AvengersAgeOfUltron'' may seem like a VillainOfTheWeek episode at first, but the events of the film have serious repercussions for the MCU, to the point of having a ripple effect (it is the catalyst for virtually everything that makes up the "Phase 3" slate in some form or another). The casualties resulting from the fight in Sokovia leads to the Sokovia Accords being established and the Avengers [[BreakingTheFellowship splitting up]] in ''Film/CaptainAmericaCivilWar'', and the main antagonist of that film [[spoiler:lost his family in the battle at the end of ''Ultron'' and wants revenge]]. By the time ''[[Film/AvengersInfinityWar Infinity War]]'' starts, the heroes are still divided, which WordOfGod says [[TheBadGuyWins is why Thanos won]]. Even in more self-contained films like ''Film/SpiderManHomecoming'' and ''Film/AntManAndTheWasp'', and television shows like ''Series/AgentsOfSHIELD'', the Accords have an impact.
*** ''Age of Ultron'' is also the point where the original team disbands and Cap's Avengers team takes over. It isn't until ''Film/AvengersEndgame'' that [[PuttingTheBandBackTogether the band truly gets back together]].

* ''Fanfic/TheBoltChronicles'': “The Wedding Reception” proves to be the catalyst for shipping Bolt and Mittens in a later fanfic. Made clear in “The Ship,” where this earlier story’s [[DanceOfRomance dance between the two characters]] is referenced as an establishing factor for Mittens’s growing attraction to Bolt.

->''"...I've been stuck in the Quantum Realm since ''Film/AntManAndTheWasp'', and guess what, the events of that film contain the secret to solving this entire decade-spanning narrative arc! In other words, FUCK ALL Y’ALL WHO DIDN’T SEE MY MOVIE, UNNECESSARY FILLER MY TINY ASS"''

* ''ComicBook/SevenSoldiersOfVictory'': Creator/GrantMorrison's ''ComicBook/SevenSoldiers'' series consists of seven miniseries that all initially seem to be telling different stories, but ultimately overlap. Also, the Leviathan, a monster made up of hundreds of feral kids that appears in one issue of the ''Klarion'' mini-series, later turns up in ''[[ComicBook/BatmanGrantMorrison Batman Incorporated]]'' as a sinister organization.

** The ''ComicBook/SecretWars1984'' Crossover contains a small subplot where Spider-Man's costume is damaged and he needs to get a new one. He finds a neat black costume that enhances his powers and looks a bit like the newly-introduced Julia Carpenter's. Just an excuse to get the character a new look, right? Well, yes, until later when the black look proved unpopular and the writers needed to walk back on that decision, which they chose to do by revealing that the black costume was alive and making it a significant member of Spidey's rogues gallery as ComicBook/{{Venom}}.

** The ''ComicBook/SecretWars1984'' Crossover contains a small subplot where Spider-Man's costume is damaged and he needs to get a new one. He finds a neat black costume that enhances his powers and looks a bit like Jessica Drew's. Just an excuse to get the character a new look, right? Well, yes, until later when the black look proved unpopular and the writers needed to walk back on that decision, which they chose to do by revealing that the black costume was alive and making it a significant member of Spidey's rogues gallery as ComicBook/{{Venom}}.

** One of the biggest instances of this was Season 3's "Let's Get Together", which contained a random joke about there being only forty-nine states and Florida not existing for some reason. Season 10 reveals that this is because [[spoiler: the Director sunk Florida so that no one would notice the disappearance of Agent Florida, also known as Captain Butch Flowers]].

** For the first Hascon, Magic released a set of cards representing other Hasbro properties. One of these was for [[Franchise/{{Transformers}} Grimlock]]. One side was a Dinosaur (a then unused type), and it was three colors: red, green, and white. Since it's silver bordered (non-canon and not legal in official events), no one thought much of it. But a couple of months later, Ixalan was released, where Dinosaurs were a major theme, and they were in red, green, and white.

* In ''Literature/ATaleOfTwoCities'' there is an early chapter that concerns a young lad observing a grave robbing. It's very atmospheric but has no connection to the plot whatsoever. Until a few hundred pages later when it is absolutely vital. Considering Dickens wrote his books as serials that's some top quality plotting right there.