Confidence is, after all, the way that we view our ability to act upon the world. If we believe that we possess significant power over our surroundings, then we have a good quantity of confidence. If we see our selves as powerless, then we have little confidence.
Confidence is meant as a way of correcting a vision impairment native to humanity.
Try as we might, we cannot see ourselves from a reasonably rational perspective. We cannot accurately estimate our abilities, our experience, or how we are viewed by the world around us. The view from Amherst is neither more nor less correct than the view from your hometowns. Nevertheless, we humans are lousy at estimating ourselves accurately, and so we have confidence to handicap our conclusions. Our level of confidence gives us a general assumption from which to work.