History JustForFun / HowToStopTheDeusExMachina

* '''Mental:''' Heroes or villains may be further constrained from taking an action by, put bluntly, not thinking of it. They might not be that bright, or their personality (see above) isn't an observant or creative one. Or if they are book smart, they aren't clever or deductive, so they put the clues together or come up with a foolproof plan. Then again, a clever, fly-by-the-seat-of-my-pants type might be too much of TheDitz to use their short term genius to problems that aren't immediate, or a meticulous [[TheChessmaster Chessmaster]] [[SpannerInTheWorks can't predict]] [[DidntSeeThatComing the unpredictable]]. Other sure fire ways of doing this are to give them a distraction: a DistressedDamsel who [[DistractedByTheSexy keeps them occupied]] intentionally or not, or a villain manipulating them into a MacGuffinDeliveryService, so they don't think to question if they're doing the right thing.

* Lina Inverse from ''Literature/{{Slayers}}'' can perform the Giga Slave, a spell which is literally capable of destroying ANYTHING, including gods. The reason she doesn't perform it more often? Because destroying anything is just a small subset of what the spell is truly capable of doing, which is [[ApocalypseHow destroying everything.]] This is generally handled fairly well in the story, with the spell and Linas ability to cast it introduced surprisingly early on, and it's use is a central plot element to the first three seasons. [[spoiler: In season one, after she performs it, a [[CloningBlues Copy Rezo]] wants it cast at him so that he can prove he's stronger than the original. She manages to find an alternative solution, however. In season two, the entire point of the events of the story was to manipulate Lina into casting the spell so that one of the settings strongest demons can bring about TheEndOfTheWorldAsWeKnowIt. In season three, it is never actually cast, but a large portion of the season is built around finding another way to defeat the BigBad that isn't nearly so risky to existence. Even as they are preparing their 'safer' alternative, it's still mentioned that if their plan doesn't show any sign of working, she's ready to cast the spell as a last resort.]]

The geographical area the hero is in can be used to make their choices a lot more limited. The section ''How to keep a character from leaving'' already details how to use it to cut them off from escape and help, but the environment can also be used to make things like fighting, thinking, or even talking hard if not impossible. All you have to do is arrange it so that what you don't want them doing is naturally impossible. For example: two if the hero could normally beat up or catch their enemy, having the hero run into the bad guy in a night club full of strobe lighting, [[FacelessMasses lots of]] InnocentBystanders, and impossibly loud music makes it a lot harder for the hero. To that end, consider engineering the story or scene to take place somewhere that is hard to see, hear, or think in (the aforementioned club would be a poor place for any hero in his cups to make an important decision).

** ''Example:'' [[LightNovel/TrinityBlood Father Abel Nightroad]] is a [[FoodChainOfEvil vampire eater]], and could easily mop the floor with most anyone. However, he enjoys being treated like a human and limiting collateral damage, so he usually accomplishes missions from behind a veil of ObfuscatingStupidity.

* In ''LightNovel/ReZero'', Subaru's life would be a lot simpler if he just told people about his Return by Death ability. Problem is, he can't due to the Witch's interference, which almost literally paralyzes him with fear whenever he tries. At one point he even decides he's going to just power through that fear and tell someone anyway, but the Witch retaliates by ''killing the person he was going to tell''. He's not keeping it a secret out of a belief that his friends can't handle the truth, a lack of faith in them, or even a fear that he won't be believed — there is a force that is very deliberately stopping him from telling anyone.
* Lina Inverse from ''LightNovel/{{Slayers}}'' can perform the Giga Slave, a spell which is literally capable of destroying ANYTHING, including gods. The reason she doesn't perform it more often? Because destroying anything is just a small subset of what the spell is truly capable of doing, which is [[ApocalypseHow destroying everything.]] This is generally handled fairly well in the story, with the spell and Linas ability to cast it introduced surprisingly early on, and it's use is a central plot element to the first three seasons. [[spoiler: In season one, after she performs it, a [[CloningBlues Copy Rezo]] wants it cast at him so that he can prove he's stronger than the original. She manages to find an alternative solution, however. In season two, the entire point of the events of the story was to manipulate Lina into casting the spell so that one of the settings strongest demons can bring about TheEndOfTheWorldAsWeKnowIt. In season three, it is never actually cast, but a large portion of the season is built around finding another way to defeat the BigBad that isn't nearly so risky to existence. Even as they are preparing their 'safer' alternative, it's still mentioned that if their plan doesn't show any sign of working, she's ready to cast the spell as a last resort.]]

* In ''LightNovel/ACertainMagicalIndex'', Index has a magical robe called the Walking Church that renders her immune to virtually all attacks. One of the first things that happens is Touma destroys it to prove the power of his AntiMagic right hand.

** '''Internal:''' Give them a sense of obligation or indebtedness, or some other emotional reason to stay. If they're helped by a GoodSamaritan, [[ThePowerOfLove fall]] for a [[HookerWithAHeartOfGold soiled dove]], a DeterminedWidow, or any other LoveInterest, or the antagonist [[ItsPersonal makes it personal]] are all good reasons (note that if they are staying to help, you need to give the person being helped a reason to stay, too, so we don't ask why the hero didn't just bring them along while he left).

* ''Literature/TheDresdenFiles'' generally takes pains to have Harry explain why he can't use certain spells or abilities or resources. One of the more common limitations is when Harry is dealing with either humans or monsters who've taken human shields, as the First law of Magic is that you ''cannot'' kill a mortal with magic directly. Other Laws of Magic deal with other particularly nasty uses of magic, such as [[BalefulPolymorph transforming bodies,]] [[MindControl mental magic]], or binding living creatures to one's will. Other times, Harry specifies that while he would ordinarily use a type of magic or call someone for backup or information, but he can't for a particular reason.