I can't speak for anyone else, but I imagine it has more to do with your upbringing than the actual quality of your body. Though being 'self-conscious' has negative connotations, it can work in someone's favor, not just being aware of the flaws but seeing the positive aspects of yourself as well. I'm extremely self-conscious, though I try not to vocalize my insecurities because I know quite a few people think I look better than I believe I do. Internalizing my percieved flaws makes me seem a lot more confident than I am, too, and allows me to focus on what I like about myself. Once you recognize what flatters you, you can play up to it, though I clearly don't always get it right (ie Vampi).