As we get older, why is it in our nature to become independent? Relying on our parents doesn't make us happy but working hard toward something does?

If parents have done. Their job well, their children will grow up and be ready 2become independent. U r right that when we become self reliant and work hard 2 achieve things we feel happier. Actually human beings take longer 2 reach independence than other mammals. Civilized modern life requires more education 2 b ready 4 independence. This may be part of human nature or learned behavior or a combination of the two.
Please Clarify. Why are you asking us a question you have already answered? It seems that you already have figured out what it means to grow up and become an adult.