I recently read an untested idea that there are two mechanisms in the human brain that affect how we act when it comes to confidence. The first evaluates whether others see us as dominant, alpha, high-status, high-value, confident, leading, whichever other term you want for it, or beta, submissive, low-status, low value, following, etc. From this it makes a guess as to where we are on the social hierarchy overall.

When the guess is that we're high on the hierarchy, the bits of the brain that allow the associated behaviors are enacted, so we act more confident, alpha, etc. And vice versa.

This model gels with the ideas of momentum, inner game as a whole, and many of my personal experiences with confidence with different people. If you can't view yourself as high-value and awesome, you're going to have a tough time acting it since that way of thinking will be virtually closed off to you.