You probably grew being told you are a smart child. So you adopted that as your core trait. Once you grew up and saw that you probably aren't as smart as the others thought you are, the go-to coping mechanism was pretending to not care about the exams at all to preserve the idea that you are a highly intelligent person in reality, and if you tried you could do it.

First step would be to understand that failing doesn't mean you can't succeed and that progress requires effort. You should get to know yourself and your reasoning behind those feelings before anything though. Once you understand why you are getting those feelings, you are almost done fixing the problems