The Precise Anatomy Of A Joke
A joke is actually a form of tension management. The humor succeeds only if the narrative builds suspense perfectly until the final second, ending abruptly before that tension can be released.
To be effective, a joke must be told with strict timing to ensure the punchline hits right at the peak of expectation. Unlike poetry, which requires exact wording, a joke is fluid oral literature that changes every time it is retold. The punchline serves as the sudden trigger that resolves the built-up curiosity through irony or wordplay. If you add even one extra sentence after the punchline, the entire comedic effect often evaporates.
Source: Joke