There is no 'secret' to personal confidence. The trouble comes as a product of society, when one compares oneself to others. It's a result of the unspoken social pecking order.
Poker is a game that takes the essense of this and turns it into a game. The winner isn't the person with the strongest hand, it's the person with the most confidence.
The bugger is that it's rather difficult to break out of the self-evaluation though, because in order to be a part of society you have to play by the rules, or get branded an outcast.