Surely You're Joking, Mr Gates

http://www.sellsbrothers.com/Posts/Details/12395

The premise is Richard Feynman applying for a job at Microsoft:

Interviewer: Here's the question: Why are manhole covers round?

Feynman: They're not. Some manhole covers are square. It's true that there are SOME round ones, but I've seen square ones, and rectangular ones.

Interviewer: But just considering the round ones, why are they round?

Feynman: If we are just considering the round ones, then they are round by definition. That statement is a tautology.

Very nice. Read the whole thing.