Once we get to the end of the novel, we understand Boo a little bit better. From the beginning, we know that people at least thought he was terrible. They thought he was a peeping-tom, an evil phantom, and a literal enemy of the police. I think Jem and Scout undergo just a little bit of persecution themselves from other members of society. Miss Caroline doesn't think the best of Scout, and Mrs. Dubose doesn't think the best of Jem. Aunt Alexandra thinks Atticus will never raise them right. Boo can relate to being misunderstood. This may indeed motivate some of his passion to help the children the evening that Bob Ewell tries to hurt them. Prior to the ultimate saving, there are many instances in which Boo may have influenced the children's safety. There is the blanket at the fire and the thought that the person in the back of the house that night was a "white" nigger. Boo loves the children and likely misses his own childhood and the opportunity to live out in front of everyone.