Whether you believe in something or not, it is still up to you. Nobody can force you to believe in something, even if they explain a lot of things about the idea that they are trying to instill in you, it is still your decision to believe them.
You believe them because you don't want to question your beliefs. You believe them because you don't believe your belief, at some point you give your belief a benefit of a doubt. But at the end of the day, if you don't believe your beliefs then it will not come true.
You can choose whatever it is that you wanted to believe. Even if you are smart, if you believe them that you are stupid then you will become stupid. You cannot escape the power of belief, it can turn a fake into reality. If you believe them that you are weak even if you are strong then you will become weak. Your mind will be programmed, your body will follow your thoughts.
So you have to be careful on what you choose to believe. Never believe an idea that is not helpful to you. Only believe in ideas that are positive, empowering and can make you keep going.
Some people are very strong, some people are very skilled and has a lot of potential but they let people's negative beliefs towards them enter their minds. The result is they became weak and they fail.
But there are some people who were below the average but thought of themselves as winners. The result is they became winners even if they don't have the necessary skills to win. That is the power of belief, it can turn things around, it can create miracles, it can change your life.
So just keep believing in yourself, believe that you can win even if you are scared. believe that you are strong even if you are weak. It is much better to have a strong and positive belief than to have weak and negative one.