Speaking from my own experience (which is the only one I have, so take or leave it if it is relevant to you), I made a conscious effort to nurse my ego and self-confidence to ridiculous levels after my experiences until age 18 conspired to squash me like a bug. My "cockiness" (as Marcus refers to the gap in the self-assesment issues) is entirely an artificial structure. And if it is reenforced by reward, it also has been structured to take some very nasty hits.
I anticipate many people will tell me why my ability to do this is linked to my being male. Very true. Which is why my experience may or may not be of value (but it's the only one I have, and as previously stated I have learned to not be shy about puting it out). But I remain fascinated by the connection between the self-construct, the societal reenforcement, and the interaction between them. It also reenforces for me the value of research to target the right problem.