Step-by-step explanation:
In movies, you always see this character who has a background where it's kinda sad and everything. In return that character acts cold around others because that's how they were treated for most of their life. Then his/her character development usually turns out for the better.
Ex) Dean was raised in an abusive home, and he treats others the same way his parents acted near him. Then he meets a group of friends that want to be friends with him, and at first he's mean, but then he turns nice in the end.
It really doesn't matter, but authors usually always include a character that has character development throughout the book/movie/etc.