Why is confidence so powerful?

It gives us a feeling of control. Marshal Goldsmith explains: People who believe they can succeed see opportunities, where others see threats. They are not afraid of uncertainty or ambiguity, they embrace it. They take more risks and achieve greater returns. Given the choice, they bet on themselves. Successful people have a high "internal locus of control." In other words, they do not feel like victims of fate. They see their success as a function of their own motivation and ability — not luck, random chance, or fate. They carry this belief even when luck does play a crucial role in success.
— Marshal Goldsmith(resource) Eric Barker, Barking Up the Wrong Tree