An engineer, a physicist, and a mathematician are trying to set up a fenced-in area for some sheep, but they have a limited amount of building material. The engineer gets up first and makes a square fence with the material, reasoning that its a pretty good working solution. No no, says the physicist, theres a better way. He takes the fence and makes a circular pen, showing how it encompasses the maximum possible space with the given material.

Then the mathematician speaks up: No, no, theres an even better way. To the others amusement he proceeds to construct a little tiny fence around himself, then declares:

I define myself to be on the outside.