I think you have to really like yourself to build up confidence that, whether you succeed or fail, make mistakes or are "perfect" it all is good. You have to be interested in yourself and cheering for yourself and trying to help yourself as if you are your own best friend (which, if you think about it, you technically should be since you're your own self and there's nobody else in your Life :-)

I think we generally lose confidence because somewhere along the line someone else said we weren't good at something or couldn't do something or had some other criticism and we believed them instead of looking at what we wanted, what the circumstances were and what we were trying to achieve, etc. Other people humiliating us does not make us worthy of humiliation! Because other people point out things they don't like about us, they don't know our story/why we do what we do or what we are working on, etc. so they don't really have the "right". Criticism is often not about us at all but about the person criticizing. And the self-critical voice we all have is usually just left over criticism from parents or teachers from when we were young and did not understand how to judge just criticism, how to use it or dismiss it as not useful to ourselves.