I'd say having determination to succeed. I had terrible self-esteem in junior high and high school and it manifested itself in 'rebellious' ways. However, I was very smart and it kind of got on my nerves that people (my dad, other kids, teachers) seemed to expect me to fail. In college, I made a fresh start and worked my *** off to get good grades, build a resume of marketable skills, develop better social skills, take better care of myself, and to not project anything that would mark me as someone with esteem problems. Meaning, I toned down the goth clothes (although it wasn't called goth back then), worried less about whether I was conforming, not conforming, blending, standing out... I just started BEING. After college, I saw what I could achieve and the rewards that could be had if I conducted myself well and always did a good job. The self-esteem naturally followed. However, as I said earlier, a lot of it just came with growing up and losing my immaturity.