Because most viewers have basic common sense, one would usually expect the same from characters on TV shows. 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. Taking this to the next level, where a character dies or very nearly dies because of their stupidity, is being Too Dumb to Live.
Can also be a response to ineffectual contestants on a Game Show.
And please, as tempting as it is to defend your favorite show from forcing the Idiot Ball into its characters' hands, refrain from making Justifying Edits. With a Card-Carrying Villain or Idiot Hero, a few of these are to be expected. If the entire show has an Idiot Plot, it goes on that page instead. Also, do not assume that something listed here automatically makes it a bad episode; it is usually more along the lines of "something else that is better could have been done". And, of course, some characters are supposed to be idiots, 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.
Compare: Idiot Ball and Villain Ball.
There are also other examples which do not fit the standard idiocy.
Warning: Spoilers ahead!
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