Sometimes anecdotes are funny or effective because they interrupt an important moment. Imagine a big wedding dinner on a TV sitcom. The best man is giving a speech, when suddenly another guest, clearly drunk, stands up and yells:
That reminds me of a wild party I went to with the groom, before he got that new ball and chain! If you had told me back then that he would choose just ONE woman, I never would have believed it!
The audience laughs at his drunken anecdote, while the bride looks at the groom in anger. Here, the anecdote brings both humor and tension to the moment.