The idea of how you see yourself is formed in childhood. We form this idea of ourselves from the responses and interactions we receive from our parents, grandparents or aunts and uncles. Later, this expands to teachers and peers.
The culture of performance and competition is unknowingly created by parents and teachers, where our worth is measured according to how we please them. When we demonstrate behaviour that pleases them, we are praised. When we do not, we are reprimanded, punished or worst of all, ignored.
We learn that we are valued and loved when we perform well and please others.
This then can form an idea that you are amazing, lovely, lovable, the best thing since sliced bread. Or, you form the idea that you are not good enough, a mistake, ugly, will never amount to much, unworthy, inadequate, etc.