"Because the plot needed it so".
That's the default answer for some questions on the [[Headscratchers/HomePage Headscratchers]] section. Questions such as:
* Why didn't Anderson do Y instead of X, that gave chance to Ben to foil his plans?
* Why didn't Alice just tell Bob that "Y" meant "You", not "Year" right at the start?
* [[WhyDontYouJustShootHim Why didn't the villain just shoot the hero with a gun]]?
And if you want to go Smarty Pants on us, the more cynical version of the answer is: the writers decided to put it there (and as far as fiction goes, they are gods).
See also the AnthropicPrinciple and the TheoryOfNarrativeCausality, and always bear in mind the MST3KMantra.
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Except if you're in RealLife. Then the answer may be:
* RealityIsUnrealistic.
* Nature just doesn't work that way.
* "People are tricky" -- Aimee Mann
* Because you touch yourself at night. "When I think of you, I touch myself." - Divinyls
* People are stupid.
* "Donald, when someone asks 'Why do they?' or 'Why don't they?', [[MoneyDearBoy the answer is almost always, 'Money']]." - Maureen Johnson, in Creator/RobertAHeinlein's ''Literature/ToSailBeyondTheSunset''
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See also: IdiotBall. Yeah, now you know. AndKnowingIsHalfTheBattle.
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