Is it necessary to know why I believe something before I can change a belief that isn’t helping me?
That may be the best question anyone could ask. The answer is no, you don’t necessarily have to know why. Some people will be able to identify some reasons or develop some hunches, though, with a little digging.
For instance, maybe you raised to focus on your flaws or to believe that self-esteem is a problematic quality. Many well-meaning parents believe it is their job to point out their children’s flaws to help the child do well in the world. Some families or communities believe that self-esteem is equivalent to narcissism and thus incompatible with humility. Or maybe there was a sense of “never good enough” in your family growing up, where the focus was on how much better you could be.
In those situations, parents and communities are often short on praise and long on critical or constructive feedback, which then becomes the norm for a child. If you grew up in an environment like that, you may have difficulty seeing or believing in your goodness or your worth. Those thoughts and beliefs simply haven’t been cultivated in your lived experience.
You may not be as easily able to answer “why” you struggle with self-confidence, though. Instead of spending a long time being critical of yourself for that, you could instead spend time intentionally nurturing beliefs that will help you become the person you want to be.