Impostor syndrome

Regardless of what level of success they may have achieved in their chosen field of work or study or what external proof they may have of their competence, those with the syndrome remain convinced internally they do not deserve the success they have achieved and are actually frauds. Proof of success is dismissed as luck, timing, or as a result of deceiving others into thinking they were more intelligent and competent than they believe themselves to be.

--Impostor syndrome via Wikipedia via Hacker News Comment
via Dustin Curtis's blog post about The Rich and Powerful

The existence and recognition of the existence of such a syndrome can also lead to delusion / inflated ego. Just as some people really have achieved great things by their own talent and merit, some people certainly have succeeded through luck alone. Well, at least once. =)