Self-confidence and the ability to believe in yourself do not come easily, but certainly are attainable. I can tell you this from personal experience. As a matter of fact, I am a walking proof that no matter how little you think of yourself, if your motivation is strong enough, anything is possible.
In psychology, there is a never-ending debate on which affects us more, nature or nurture? On the one hand, we are born with a number of traits and behaviors that feel more natural to us, but on the other hand, we are heavily influenced by our surroundings. In the case of self-confidence and the ability to believe in yourself, both nature and nurture were against me.