Jerry Seinfeld compares telling a joke to attempting to leap a metaphorical canyon, taking the audience with him. The set-up is the nearside cliff, and the punchline is the far side. If they're too far apart, the listeners don't make it to the other side. And if they are too close together, the audience just steps across the gap without experiencing any exhilarating leap. The joke-hearer gets far more pleasure from the joke if he or she has to do a little work.
The surprise mechanism doesn't work without effective timing. It's almost impossible to explain in print because our eyes always skip ahead to the punchline before the set-up is properly digested. But next time you listen to a comedian, listen to the pauses. They're not that funny on their own - obviously, they're just tiny silences - but the point is, neither are the jokes.
It's not that long, wordy jokes can't be funny, but if too much is explained, there's no logical leap for the audience to make, and the paradigm shift which elicits laughter is lost.
Compare: I'm not a homosexual. Mind you, I might be mistaken for one if I went to the north of England. In places like Newcastle, there's such a culture of macho posturing that they go out in their shirtsleeves in all kinds of weather, so if you wear a coat they think you're gay.
And: I'm not gay. Unless you're from Newcastle and by 'gay' you mean, 'owns a coat'.
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