HEALTH:

The only way Bruce becomes the Hulk is if he gets mad about something. Because of that which is not good, he usually gets low self-esteem because the experiment ruined his life. But since that experiment happened, he tends to live on and tries to keep positive thoughts without turning into the Hulk by trying to help save the world later on with the Avengers. This way he can have both negative and positive self-esteem about himself.