If they approve of us, then we're worth more. And these seeds were sown when we were children. As we grew up, most of our parents made us feel more worthy if we performed well. This carried into school and on into the workplace. If we perform well at work, in most cases we're rewarded with higher pay and more responsibility.
Problems start for some people in elementary school.
There are children who simply cannot perform at a rate equal to the rest of the class, and many times it'll be due to teaching methods or plain old loss of confidence due to the child's having been harangued and harassed by his peers. He'll be the last one chosen when the class math captains are picking their teams, and if anybody is going to make a mistake and blow the spelling bee for his team it'll be him. These children frequently do far more poorly in school than they should, and the lack of approval they experience at the hands of their peers is at the root of the problem. They begin to believe that they were born to fail, and because this program has been written into their minds by others, they zero in on the negative feedback about their performance. Even when positive feedback comes, they discard it in their minds as false, and it has taken years and much emotional trauma for them to develop this mind-set.