When you don't know what you're talking about, it's hard to know when you're finished.

The joke turns on a paradox: ignorance doesn’t merely prevent someone from speaking accurately; it also deprives them of the internal “stopping rule” that signals completion. If you don’t grasp the subject, you can’t tell when you’ve covered it, when you’ve contradicted yourself, or when you’ve drifted into irrelevance—so you keep talking. Beyond humor, it’s a critique of bluster and overconfidence, especially in public discourse, where verbosity can masquerade as expertise. Implicitly, it praises genuine knowledge as something that brings clarity, structure, and restraint—knowing both what to say and when to stop.