This ties in to an amazingly important (and rare) personal characteristic: self-awareness. Being able to honestly identify your own strengths and weaknesses is the only way to systematically build the former and eliminate the latter.
In my experience, few people are able to assess themselves effectively; it's too easy to slide in one of two directions: avoidance or neurosis. But as the saying goes: the unexamined life is not worth living.
Self-analysis can sometimes precipitate a cycle of anxiety and doubt. Some people can leverage this constructively and use it as motivation, but for others it's destructive.
I tend to think those people who seem crippled by self-doubt see just as distorted a picture of themselves as people who are incapable of self-examination, just skewed the other direction. Minimization vs maximization of faults.
In my experience, few people are able to assess themselves effectively; it's too easy to slide in one of two directions: avoidance or neurosis. But as the saying goes: the unexamined life is not worth living.