I am a dentist

Trying to find things to destract myself from my infantile dependence on LOST and my ebullient enthusiasm pertaining to the season premiere of season 4 thursday night, I agreed to participate in a psychological study regarding the nature of friendships. I forgot what it was about, but I remember one of the questions dealt with self-confidence. I also remember my response to the question - do you have any self-confidence? ... I wasn't sure how to respond. Under some circumstances I am brimming with self-confidence and feel quasi-indestructible. However, at other times I feel like a steaming pile of $hit. So which am I?