I believe confidence is derived from competence. People often say just believe in yourself. Well, it's hard to believe in yourself if you're not sure you can make it. To be sure you can make it, you need enough experience and hours of practice. And that's where feeling of competence starts to awake. Next step is being acknowledged by professionals in a field you want to master. When they say you're really good then confidence will sneak in naturally. Nothing is as powerful as your experience. More you have it, more confident you're going to be. Put yourself out there an life will teach you.