Idiom
have something to prove
to need to show that you can succeed when people expect you to fail.After two dismal seasons, the players on this team feel they have something to prove.
Usage notes: also used in the negative form have nothing to prove or not have anything to prove - to have no reason to persuade others you can succeed, because you have already succeeded:
He was as famous as he wanted to be, and felt he no longer had anything to prove.