Because most viewers have basic common sense, one would usually expect the same from fictional characters. Any negative deviation from such usually prompts a Face Palm and the comment "What an idiot!" or similar, hence the entry name.
Can cause A Tragedy of Impulsiveness, if the situation becomes more serious. It is also the usual reaction to a character demonstrating especially severe Genre Blindness.
And please, as tempting as it is to defend your favorite work from forcing the Idiot Ball into its characters' hands, refrain from making Justifying Edits. With a Card-Carrying Villain, Smug Snake, or Idiot Hero, a few of these are to be expected. Also, do not assume that something listed here automatically makes it a bad work; it is usually more along the lines of "something else that is better could have been done". As explained on Idiot Ball, characters being idiotic can often serve as a weakness to them and sometimes make them more-or-less well-developed. And, of course, some characters are supposed to be idiots (or outright naïve at best), in which case we probably don't need a full and complete list of every stupid thing they do; a brief summing up would be more helpful. Characters making foolish decisions can also result in funny or dramatic moments, and therefore add to the enjoyability of a work; so writers can and have invoked this trope intentionally.
- 1-Dimensional Thinking: A character tries to avoid a non-sentient object hurtling towards them by outrunning it, instead of simply jumping to the side and letting it pass.
- Because I Said So: An authority figure believes they are entitled to unquestioning obedience without having to explain why the rules they set should be obeyed, obliviously creating a Forbidden Fruit effect.
- Better to Kill Than Frighten: Why bother using fear and manipulation to ensure compliance when you can just murder dissenters instead? It creates far more problems than it solves.
- Bond Villain Stupidity: An antagonist has the opposing side at their mercy... and stops to gloat about their imminent victory instead of just dispatching the opposing side while they have the chance, usually resulting in an easily-avoidable escape.
- Boss-Arena Idiocy: This video game boss is completely undefeatable... or at least they would be, if not for convenient circumstances within their own arena that can be used against them.
- Bullying a Dragon: See that person/animal that can seriously injure and/or kill us? Pfft, what an inferior being! Let's insult and throw rocks at them!
- Deer in the Headlights: A character freezes in fear as they're being attacked.
- Devil in Plain Sight: A character is Obviously Evil to the audience, but only a select few other characters distrust them; the rest suspect nothing.
- Dick Dastardly Stops to Cheat: This antagonist would have succeeded if they hadn't tried to do something evil.
- Didn't Think This Through: A character comes up with a plan which has a serious flaw they don't realize until it's too late.
- Drunk Driver: A character drives after drinking alcohol, to disastrous results.
- Failed a Spot Check: A character doesn't notice something important or obvious, even when it's right in front of them.
- Forgot About His Powers: A character who is in trouble has powers that could get them out of it or at least help a lot, but they don't think to use them.
- Greed Makes You Dumb: A character is so focused on gaining more money, power, etc. that they make short-sighted decisions.
- The Guards Must Be Crazy: Idiotic guards make it easier for the imprisoned to escape.
- Horrible Judge of Character: This character trusts someone who others suspect is not trustworthy (at best)* and/or is Obviously Evil (at worst).
- Idiot Ball: An otherwise-competent character does something stupid for the sake of plot convenience or Character Development.
- Leeroy Jenkins: An impulsive combatant decides to make a full frontal assault when the situation doesn't call for one, ignoring orders and/or more pragmatic tactics.
- Lethally Stupid: A character makes a decision that is so idiotic it causes others to get seriously injured and/or killed.
- Nice Job Breaking It, Hero: The hero's actions unwittingly help the villains.
- Nice Job Fixing It, Villain: The villain's actions unwittingly help the heroes.
- Paper-Thin Disguise: A (usually shady) character does such a poor job at disguising themselves that their identity is incredibly obvious to the audience. However, the other characters don't recognize them.
- Poor Communication Kills: A character doesn't disclose — or worse, actively withholds — important information, with disastrous results.
- Revenge Before Reason: This character has suffered a lotnote , but they allow the desire for Revenge against those who have hurt them to override their common sense, creating far more problems than it solves.
- Skewed Priorities: When someone prioritizes something when there's clearly another matter that they should be focusing on instead.
- Tactical Suicide Boss: This video game boss is completely undefeatable... or at least they would be, if not for one (or more) of their own attacks exposing their weak point which you can attack for massive damage.
- Too Dumb to Live: A character makes a decision that is so idiotic it causes themselves to get seriously injured and/or killed.
- Villain Ball: An otherwise-competent antagonist does something stupid for the sake of being evil.
- Stupid Evil: This antagonist, on the other hand, grabs the Villain Ball so often that it's a surprise they haven't caused their own death already, and it's not a surprise if they eventually do.
- What Could Possibly Go Wrong?: This character is far too confident in The Plan's success for their own good, neglecting to take any precautions.
- Why Don't You Just Shoot Him?: A character tries to dispose of another in an Awesome, but Impractical way.
There are also other examples that do not fit the standard idiocy.
Warning: Spoilers ahead!
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