From an O.Henry short story:
"Man is too thoroughly an egoist not to be also an egotist; "

An egoist has a good opinion of himself, an egotist flaunts it.

If one generally had a bad opinion of oneself, how could one go forth and accomplish anything?

That said, some study (aren't there too many?) showed that criminals in federal penitentiaries held by far higher than average ego ratings.