Problems tend to come in five varieties:
# '''Known Knowns''' (known of and known about): There are the dangers you deal with directly: My opponent has access to [[EnergyWeapon laser blasters]] -- I need DeflectorShields before I attack.
# '''Known Unknowns''' (known of, but not fully known about): These are the things strategists know they don't know, but they can prepare for the different possible outcomes: The enemy has his forces deployed elsewhere when you are StormingTheCastle, so you need one plan for what to do if these forces do not return in time (to take full advantage), and you need another plan for what to do if these forces do return in time (to avoid getting trapped in a pincer). Someone who is especially good at this kind is probably CrazyPrepared or a master of XanatosSpeedChess.
# '''Unknown Unknowns''' (neither known of nor known about): These cannot be prepared for, planned for, or in any way anticipated. They are the bane of all well-laid plans. This can often be a GenreShift, for example, and the character was in the dark because of the {{masquerade}}. The mage being surprised by the space alien, for instance, or TheMafia [[Manga/DeathNote not expecting]] PsychicPowers. [[DiabolusExMachina Acts of God]] and {{Outside Context Problem}}s tend to fit in here, unless characters are aware that they are a CosmicPlaything, and even then it's hard to know what you don't know, except that you don't know anything.
# '''Unknown Knowns''' (known about, but not known of as a threat): It happens. Sometimes the plotter knows a given [[TheFool person]], event, or variable is present... but doesn't see how it could ''[[{{Pride}} possibly]]'' impact their foolproof plans and proceeds to [[NotNowKiddo dismiss it]] or [[MistreatmentInducedBetrayal mistreat those "irrelevant" to his plot]], and otherwise ignore [[SwordOfDamocles the sword overhead]] [[LaserGuidedKarma while whittling at the rope holding it there]]. In MysteryFiction, these people are the suspects and facts that are quickly [[BeneathSuspicion discarded in favor of the high-profile suspects]]. However, add up all the background chatter and the motivations for why [[TheButlerDidIt it was the butler]] becomes incredibly obvious. See TheDogBitesBack and EvilCannotComprehendGood.
# '''[[EntertaininglyWrong False Assumptions]]''' (problems with ''ThePlan itself''): Even the most diabolical scheme can be doomed before it even starts if it's built on [[PoorCommunicationKills faulty information.]] That [[WesternAnimation/{{Futurama}} ridiculously circuitous]] plan to steal the MacGuffin from the safe deposit box by sneaking into the bank disguised as security guards? The only thing TheHero's grandfather hid there was some [[AllThatGlitters old family memorabilia]]; the MacGuffin is [[YourPrincessIsInAnotherCastle hidden somewhere else entirely]] (if it even exists).

Any dangers and problems that are known to exist are possible to plan around, and thus rarely qualify for this trope.
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