Confidence is basically the measure in which you are certain of the things you say and do. It starts to grow the moment you start doing what you say and saying what you do. It requires a degree of knowing yourself, and the state of your integrity. Now I was nowhere near my current state, but did always have certain things I would just "know", without being aware of why or how I knew. It was that way when my wife and I were trying to conceive, and she doubted whether we would. She went to the doctor and was given a temperature chart, and after three dots on the chart I knew: tendency going up, and women tend to have a slightly higher but extremely constant body temperature when pregnant, so I told her. Of course my arguments just given in now way made it a proven fact, but my mind and heart knew otherwise: there was no doubt in my mind! The same thing then happened with the gender of that baby and the next one: in both cases I knew they would be girls, long before any indication was visible.
In hindsight, I feel this "knowing" is not foresight, but power of creation: because there is no doubt in our mind, and the gratitude for having that situation come true is there as well, the Grand Overall design conspires to make the situation manifest in our physical reality.