"Oh. Well, nobody knows anything about that, so I guess we can't talk about that."(From Surely You're Joking Mr. Feynman.)
"On the contrary," I answered, "it's because somebody knows something about it that we can't talk about Physics. It's the things nobody knows anything about that we can discuss. We can talk about the weather; we can talk about social problems; we can talk about psychology; we can talk about international finance--gold transfers we can't talk about, because those are understood--so its the subject nobody knows anything about that we can all talk about!"
I don't know how they do it. There's a way of forming ice on the surface of the face, and she did it! She turned to talk to somebody else.
Lichtenberg, from The Waste Books, Book E, entry 15:
What? to debate a subject you have to know something about it? It is my view that a debate requires that at least one of the disputants knows nothing of the subject under discussion, and that in a so-called lively debate in its highest perfection neither party knows anything about it or even the meaning of what he is saying. . . . When I was in England, the American question was debated in every ale-house, coffee-house, crossroads and stagecoach, and even in the council of aldermen at whose head Wilkes stood, in accordance with the rules of lively debate; and when some poor simpleton once stood up and suggested that it might be a good thing to examine the subject seriously before coming to a decision, another man expressly objected that this would be a wearisome task and lead them too far astray, and that a decision should be taken without further ado--which, because it was almost dinner time, was the course agreed upon.