http://www.paulgraham.com/gh.html is Paul Graham's latest essay, on what makes a Great Hacker. In it, he writes:

The people I've met who do great work rarely think that they're doing great work. They generally feel that they're stupid and lazy, that their brain only works properly one day out of ten, and that it's only a matter of time until they're found out.

Now if only cause and effect pointed in the other direction… :-)