Mathematicians are notorious for being sticklers when it comes to requiring absolute proof before accepting any statement. Their reputation is clearly expressed in a story told by Ian Stewart in Concepts of Modern Mathematics:

    An astronomer, a physicist, and a mathematician (it is said) were  holidaying in Scotland. Glancing from a train window, they observed a black sheep in the middle of a field. "How interesting," observed the astronomer, "all Scottish sheep are black!" To which the physicist responded  , "No, no! Some Scottish sheep are black!" The Mathematician gazed heavenward in supplication, and then intoned, "In Scotland there exists at least one field, containing at least one sheep, at least one side of which is black."

The story was from Fernat's Enigma, by Simon Singh.