Do not be rash with your mouth, and let not your heart utter anything hastily before God. —Ecclesiastes 5:2
Aren't we our own worst critics? Our thoughts are a powerful influence on how we value our own self worth. Is your thought rhetoric a positive or negative influence? Do you really listen to what you're telling yourself?
Self confidence is built by more than just a few successful endeavors. It begins with not only encouragement from others but also what you speak to yourself in your mind. 'You can't live a positive life with a negative attitude.' It also still is true from way back when that 'Can't Never Could.'
The verse above says don't be rash with your mouth but what comes out your mouth began in your head. We often say things to ourselves or about ourselves that we wouldn't dare say to someone else. Why? Belittling ourselves can become a bad habit and happen so often we don't even notice when we do it.
In bookstores there are always a 'self help' section. Start by helping your own heart and mind by being a voice of encouragement to yourself.