History Main / YouWillKnowWhatToDo

* ''Literature/{{Metro 2033}}'': Artyom is sent out by the Brahmins (who he's never met) to the Lenin Library (where he's never been) to find a lost book of prophecies (which he's never seen). They totally guarantee that he'll know where it is, though. [[spoiler:[[SurprisinglyRealisticOutcome He doesn't.]]]]

* In ''Manga/RaveMaster'', Haru Glory, wielder of the Ten Commandments sword, initially can only create the "Explosion Sword." Eventually, he is given the Rave of Wisdom, which gives him knowledge which is only gradually unlocked and told "YouWillKnowWhatToDo." From then on, he's able to [[NewPowersAsThePlotDemands whip out new forms of his sword as the plot demands.]] This comes with an understanding of ''how'' the powers work, so he can from then on also call them forth at will.

* In ''Lovely Assistant'' (by Geoph Essex), when Jenny ''finally'' gets the chance to take a lesson in [[spoiler: [[TheGrimReaper Grim Reaping]]]] from Caravel, Caravel essentially says "YouWillKnowWhatToDo" when it comes to [[spoiler: using the sword and guiding people to the afterlife]]. As it turns out, it's literally true: Jenny instinctively knows what to do when she gets there and is pretty surprised by that fact herself. (The implication that the experience is better than drugs or sex for [[spoiler: [[TheGrimReaper Grim Reapers]]]] suggests that it's just a "natural" thing for them to do, like fish swimming or birds flying.)

* ''Literature/{{Metro 2033}}'': Artyom is sent out by the Brahmins (who he's never met) to the Lenin Library (where he's never been) to find a lost book of prophecies (which he's never seen). They totally guarantee that he'll know where it is, though. [[spoiler:[[RealityEnsues He doesn't.]]]]

* ''Film/Dragonslayer'': Ulrich tells Galen to destroy his amulet -- "and me along with it...you'll know the time." Then he disappears. Later, when [[spoiler: Ulrich is snatched up by the flying dragon, Galen smashes the amulet. Ulrich explodes, taking the dragon with him.]]

* ''Literature/RhythmOfWar'' (fourth book of ''Literature/TheStormlightArchive''): Mraize tells Shallan she'll know what to do when she finds the person he's told her to locate. When she does, and discovers [[spoiler: he's one of the immortal Heralds]], she is shocked and rushes to call Mraize and complain that she had absolutely no idea what to do. He says rather smugly that she did exactly what he wanted: Contact him for further instructions.

* In ''Literature/RhythmOfWar'' Mraize tells Shallan she'll know what to do when she finds the person he's told her to locate. When she does, and discovers [[spoiler: he's one of the immortal heralds]] she is shocked and rushes to call Mraize and complain that she had absolutely no idea. As it turns out, what he wanted her to do was "Contact me for further instructions".

** The trope ends up [[SubvertedTrope subverted]] when [[spoiler: Harry trusts Karrin Murphy with ''Fidelacchius'', only for it to end up broken when she tries to use it for unjust ends. Harry believes he failed, right up until Waldo Butters, Jewish coroner extraordinare, takes up the shattered hilt of the sword and uses his faith in ''other people'' to recreate the sword as a ''lightsaber''. Harry didn't choose Butters, but the ''sword'' did.]]

Stock phrase when the hero is presented with a PlotCoupon.

* In ''Manga/RaveMaster'', Haru Glory, wielder of the Ten Commandments sword, initially can only create the "Explosion Sword." Eventually, he is given the Rave of Wisdom, which gives him knowledge which is only gradually unlocked and told "YouWillKnowWhatToDo." From then on, he's able to [[NewPowersAsThePlotDemands whip out new forms of his sword as the plot demands.]] This comes with understanding of ''how'' the powers work, so he can from then on also call them forth at will.
* This was sort of the case in ''Anime/YuGiOh'' where Kaiba gave Yugi his copy of Fiend's Sanctuary before the final battle with Marik in Battle City. Kaiba knew it was an effective weapon against the Winged Dragon of Ra, but he just told Yugi to take it and nothing else, figuring that if Yugi was capable of winning at all, he could figure out how to use it on his own. Fortunately, he did. (It's absent from the dub, but Kaiba calculated when he gave Yugi the Fiend's Sanctuary card that it would do nothing more than increase Yugi's chances against Marik from 3% to 20%; he still doubted Yugi stood much of a chance. Kaiba told Ishizu that he only helped Yugi to prove her wrong about the bond between then when he lost. At least that's what he claimed. And as stated, Yugi ''did'' win, the card helping a great deal.)
* Zigzagged in the first season of ''Anime/YuGiOhGX''. After Judai defeats Daitokuji-sensei, he gives Judai the [[TomeOfEldritchLore Emerald Tablet]] before his physical body dies. Later, before he duels [[BigBad Kagemaru]], Judai finds a card called Sabatiel - The Philosopher's Stone in the book, and figures he should add it to his deck. Just as he's at the end of his rope, he draws the card, but still has no idea how to use it. Daitokuji's spirit appears, and is about to tell him ''exactly'' how to use it, but then he's [[ItMakesSenseInContext swallowed by his cat Pharaoh]] before he can tell Judai the complete effect. Fortunately, Judai is able to figure that out on his own.

* In ''Film/GalaxyQuest'', the protagonists have to admit they don't know how the Omega-13 device works, because the TV series ended on a CliffHanger before it was actually used. Fortunately, one of the [[{{Fanon}} fan theories]] proves correct.

* In the move ''Film/LittleNicky'', a group of angels hand Nicky a white orb before his confrontation with his brother, relaying a message from the God that when the times comes, he'll know what to do. [[spoiler:It ends up summoning Music/OzzyOsbourne]].

* ''Film/CaptainAmericaCivilWar''. During the airport battle Ant-Man tells Captain America, "On my signal, run like hell." Shortly afterwards he uses his abilities to [[spoiler:grow to enormous size.]]

* ''Literature/HarryPotterAndTheDeathlyHallows'': [[PowerTrio Each child]] gets a pleasant but [[ItMayHelpYouOnYourQuest seemingly useless gift]] from Dumbledore [[spoiler:by his estate's executor]] with cryptic hints. [[TheChessmaster Each proves critical to their quest]]. Justified because [[spoiler: Dumbledore is dead and since the aforementioned executor takes anything he deems "suspicious"]] he can't outright ''tell'' them. It does however raise the question why he didn't just give it to them earlier, transfigured if necessary, since [[spoiler: he knew he was going to die almost a year in advance]]. [[BatmanGambit But hey, it's Dumbledore.]]
* Subverted in ''Literature/HarryPotterAndTheOrderOfThePhoenix''. In the beginning of the book, Sirius gives Harry a package with instructions to use it if Harry needs Sirius' help. Knowing that any attempt to help Harry by Sirius would bring with it an unacceptable risk of being captured and re-imprisoned, Harry resolves never to use it, promptly forgets about it, and doesn't consider that it could be equally useful should ''Sirius'' need ''Harry's'' help. [[spoiler: It turns out to be an enchanted mirror allowing safe, easy two-way communication between the two.]] A lot of tragedy could have been avoided if [[PoorCommunicationKills Sirius had just told Harry what it was instead of being mysterious about it.]]

* Done several times in the ''Literature/SwordOfTruth''. Prophecies given 3000+ years ago can be pretty nonspecific, you know? Additionally, the irrational use of this trope is lampshaded by Richard himself, who, as Seeker, is somehow expected to know how to solve everyone's problems. He actually ends up subverting his own lampshade by being an unusually bright and logical protagonist, and its revealed that one of the primary characteristics of a true Seeker is that they have this trope or the ability to invoke it ''before'' they get the sword.

* In ''Lovely Assistant'' (by Geoph Essex), when Jenny ''finally'' gets the chance to take a lesson in [[spoiler: [[TheGrimReaper Grim Reaping]]]] from Caravel, Caravel essentially says "YouWillKnowWhatToDo" when it comes to [[spoiler: using the sword and guiding people to the afterlife]]. As it turns out, it's literally true: Jenny instinctively knows what to do when she gets there, and is pretty surprised by that fact herself. (The implication that the experience is better than drugs or sex for [[spoiler: [[TheGrimReaper Grim Reapers]]]] suggests that it's just a "natural" thing for them to do, like fish swimming or birds flying.)

* ''Series/{{Merlin|2008}}'' had the Fisher King giving Merlin a waterglobe artifact in season 3 and telling him "When all seems lost, this will show you the way." But Merlin himself had to figure out what to do with it (and did so on accident,dropping and smashing it so the water fell into the bucket and Freya appeared.)
* In the ''Series/{{Supernatural}}'' episode "[[Recap/SupernaturalS06E11AppointmentInSamarra Appointment in Samarra]]", Death instructs Dean to keep researching the souls, and says that he will understand when he needs to. To his exasperation, Death ends up having to spell it out for Dean anyway.

* In ''VideoGame/EricTheUnready'', you pull the legendary banana "Excalibanana" out of a stone, thus proving that you are the hero chosen to save the princess. You're then instructed to throw it in the pond, so you can magically summon it forth in its time of need. Exactly what use you'll have of a banana, even a legenday one with a badass name, is not readily apparent.

* In the "Fate" story path of ''VisualNovel/FateStayNight'', Archer takes time [[spoiler:before his HeroicSacrifice]] to tell Shiro that he is a "maker" not a "fighter", and that this will save him. Of course, Archer is [[spoiler:speaking from personal experience, as he's Shiro's older self]].

* Dank from ''Webcomic/SneakyGoblins'' [[http://www.tolcraft.com/comic/page-55/ discovers]] that the pack Grimwold [[http://www.tolcraft.com/comic/page-19/ gave him near the beginning of the adventure]] is in fact a glider. [[JustInTime That was fortunate.]]

* In the episode of ''WesternAnimation/TheSmurfs'' "The Cursed Country", Hefty and Smurfette have to lead Peewit and Sir Johan to their village, which is being held hostage by a wizard and his trained dragon. The wizard Homnibus lends them a stick that can produce water should they need it; however, the first time they try to use it, they discover it produces ''salt'' water, making it unfit to drink. Later, however, [[spoiler:after waiting for the dragon to fall asleep, they realize it's true purpose: Johan cuts a small sliver of it and gives it to Papa Smurf, who is then able to crawl into the beast's belly and use it there, rendering the dragon unable to breath fire and nearly powerless.]]

* The [[GoldenSnitch amulet]] from the final episode of ''Series/BuffyTheVampireSlayer''.

* ''Series/PersonOfInterest''. [[BenevolentAI The Machine]] works entirely like this. While its human agent Root takes this [[MachineWorship entirely in stride]], the rest of Team Machine find it rather frustrating.

* Parodied by [[Website/TheBestPageInTheUniverse Maddox]] in [[http://www.thebestpageintheuniverse.net/c.cgi?u=matrix3 his review]] of ''Film/TheMatrixRevolutions'', which he hated. He particularely criticizes the {{Cryptic Conversation}}s between Neo and the Oracle.

Expect things to go badly if the character ''[[SubvertedTrope doesn't]]'' [[SubvertedTrope know what to do with it]].

* This was sort of the case in ''Anime/YuGiOh'' where Kaiba gave Yugi his copy of Fiend's Sanctuary before the FinalBattle with Marik in Battle City. Kaiba knew it was an effective weapon against the Winged Dragon of Ra, but he just told Yugi to take it and nothing else, figuring that if Yugi was capable of winning at all, he could figure out how to use it on his own. Fortunately, he did. (It's absent from the dub, but Kaiba calculated when he gave Yugi the Fiend's Sanctuary card that it would do nothing more than increase Yugi's chances against Marik from 3% to 20%; he still doubted Yugi stood much of a chance. Kaiba told Ishizu that he only helped Yugi to prove her wrong about the bond between then when he lost. At least that's what he claimed. And as stated, Yugi ''did'' win, the card helping a great deal.)

* ''Literature/HarryPotterAndTheDeathlyHallows'': [[PowerTrio Each child]] gets a pleasant but [[ItMayHelpYouOnYourQuest seemingly useless gift]] from Dumbledore [[spoiler:by his estate's executor]] with cryptic hints. [[TheChessmaster Each proves critical to their quest]]. Justified because [[spoiler: Dumbledore is dead and since the aforementioned executor takes anything he deems "suspicious"]] he can't outright ''tell'' them.
** It does however raise the question why he didn't just give it to them earlier, transfigured if necessary, since [[spoiler: he knew he was going to die almost a year in advance]]. [[BatmanGambit But hey, it's Dumbledore.]]
** Subverted in ''Literature/HarryPotterAndTheOrderOfThePhoenix''. In the beginning of the book, Sirius gives Harry a package with instructions to use it if Harry needs Sirius' help. Knowing that any attempt to help Harry by Sirius would bring with it an unacceptable risk of being captured and re-imprisoned, Harry resolves never to use it, promptly forgets about it, and doesn't consider that it could be equally useful should ''Sirius'' need ''Harry's'' help. [[spoiler: It turns out to be an enchanted mirror allowing safe, easy two-way communication between the two.]] A lot of tragedy could have been avoided if [[PoorCommunicationKills Sirius had just told Harry what it was instead of being mysterious about it.]]

* In ''TheLordOfTheRings'', Galadrial gives Frodo a phial of water from her fountain, saying "May it be a light to you in dark places, when all other lights go out". While this has an obvious literal meaning, it takes on a new significance when [[spoiler:Sam is fighting Shelob and it turns out that the light from a Silmaril is a more potent weapon against the daughter of [[EldritchAbomination Ungoliant]] than the sharpest of swords could ever be]].

* In ''[[Literature/ThePowerOfFive Evil Star]]'', the Incas give Richard a Tumi (sacrificial knife), warning him that he will regret ever having been given it. [[spoiler: In the final book ''Oblivion'', Richard uses the knife to kill Matt, sparing him from further pain and torture, and allowing past Matt to be summoned to the present.]]

->'''Reggie:''' Take this walkie talkie and hide. You'll know what to do.
->'''Twister:''' I will?

-->'''Quinn:''' I'm going out. Anything happens, you know what to do.
-->'''Creedy:''' Uh no. I have no idea.
-->'''Quinn:''' Yeah, me neither.

-->'''Neo:''' What do I need to do?
-->'''Oracle:''' You KNOW what you need to do.
-->'''Neo:''' Where do I need to go?
-->'''Oracle:''' You KNOW where you need to go.
-->'''Neo:''' Who do I need to see?
-->'''Oracle:''' You KNOW who you need to see.
-->'''Neo:''' What do you want?
-->'''Oracle:''' The same thing you want.
-->'''Neo:''' How will I know I'm making the right choice?
-->'''Oracle:''' You will KNOW...!

* Parodied in ''WesternAnimation/FamilyGuy'', where Quagmire is told this and given... [[ItMayHelpYouOnYourQuest a banana]]. Further subverted when Quagmire is running for his life, recalls the cryptic advice, and throws the banana at his attacker. It bounces off harmlessly, falls to the ground, and both parties look expectantly at it. Nothing happens, and after a moment, the chase resumes.
** Of course nothing happens, because Quagmire was too GenreBlind to do a banana peel gag. [[spoiler: Cleveland]] was probably looking at it less expectantly and more "Did he just throw a banana at me?"

Usually translates as "We're not going to tell you what the magic amulet does yet in order to keep the audience in suspense," or, more cynically, "We don't actually want to do the work to prevent a DeusExMachina ending, so we're throwing this in now to make it look like we had it planned all along." Sometimes, in a very long arc, it can also mean "We haven't worked the resolution out either, so we're tossing in a random item now. The author will work out what it's for later." [[GenreSavvy Perhaps they know]] that an [[UnspokenPlanGuarantee unspoken plan always works]]?

* ''Series/{{Merlin}}'' had the Fisher King giving Merlin a waterglobe artifact in season 3 and telling him "When all seems lost, this will show you the way." But Merlin himself had to figure out what to do with it (and did so on accident,dropping and smashing it so the water fell into the bucket and Freya appeared.)

Usually translates as "We're not going to tell you what the magic amulet does yet in order to keep the audience in suspense," or, more cynically, "We don't actually want to do the work to prevent a DeusExMachina ending, so we're throwing this in now to make it look like we had it planned all along." Sometimes, in a very long arc, it can also mean "We haven't worked the resolution out either, so we're tossing in a random item now. The author will work out what it's for later." Perhaps they know that an [[UnspokenPlanGuarantee unspoken plan always works]]?

* In ''[[ThePowerOfFive Evil Star]]'', the Incas give Richard a Tumi (sacrificial knife), warning him that he will regret ever having been given it. [[spoiler: In the final book ''Oblivion'', Richard uses the knife to kill Matt, sparing him from further pain and torture, and allowing past Matt to be summoned to the present.]]

* Episode 52 of ''ScoobyDooMysteryIncorporated'': The Annunuki, in the host body of Nova (Brad and Judy's Cocker Spaniel), tells Scooby this during the final battle with the Nibiru Entity. Scooby gets very frustrated and tells her to ''just tell him'' what to do since they are in such danger.

[[folder:Real Life]]
* Common with sex and romance. No one will tell you how they work, but it's assumed that you'll know what to do.
[[/folder]]

* Parodied in ''Film/ReignOfFire'' :
-->- I'm going out. Anything happens, you know what to do.
-->- Er... no.
-->- Yeah, me neither.

* In the move ''Film/LittleNicky'', a group of angels hand Nicky a white orb before his confrontation with his brother, relaying a message from the God that when the times comes, [[YouWillKnowWhatToDo he'll know what to do]]. [[spoiler:It ends up summoning Music/OzzyOsbourne]].

* ''Film/{{Patton}}'': "When you put your hand into a bunch of goo that a moment before was your best friend's face, you'll know what to do."
* ''Film/SupermanII''. While escaping from prison, Lex Luthor sends his brainless henchman out first. The henchman asks what he's looking for and is told, "You'll know it when you find it." Cue minion bumbling along until he encounters a rope ladder. "I found it!"