10James Potter Was Privileged
It'd be a lie to claim James Potter didn't grow up a very obviously privileged kid and it gave him a bit of an ego in school. As a child, we can safely assume James didn't know hardship. He was a pure-blood, so faced no discrimination at Hogwarts; his parents
were both rich and loving; and he was automatically popular due to his charisma.
Privilege doesn't always automatically create bad people, but it can certainly give them an inflated sense of self-importance and boy, it sure did create that in James.