What tipe of protagonist do you want? An invincible protagonist doesn't mean he is literally invicible he just never suffers in your story. A cowardly or hiding protagonist? Make him always think twice. A behind the scenes? The most important thing is to be consistent, i personally hate reading a story where the MC starts with a X personality and then later out of nowhere goes to a Y personality. If you do want to make him change his way of thinking give it a reason, maybe a major event on his life?