How to be confident/secure when you feel like you have no reason to be

I, (F21) have realized that I have lower self-esteem, and I think in some ways it holds me back from enjoying my life as much as I could, because as successful as I could be, etc.

I guess my question is always: “Why should I be confident if I don’t have a reason to be?” I am average looking, I have an average IQ, there are people with more natural talent than me, etc. So why should I be secure when there is always going to be someone that is better?