When the scientist tells you he does not know the answer, his is an ignorant man. When he tells you he has a hunch about how it is going to work, he is uncertain about it. When he is pretty sure of how it is going to work, and he tells you, "This is the way it's going to work, I'll bet," he is still in some doubt.

The Meaning of It All, Chapter 1 (p. 27), Addison-Wesley. 1998