Suppose there is a town with just one barber, who is male. In this town, every man keeps himself clean-shaven, and he does so by doing exactly one of two things:
Shaving himself, or
going to the barber.
Another way to state this is:
The barber shaves only those men in town who do not shave themselves.
All this seems perfectly logical, until we pose the paradoxical question:
Who shaves the barber?