Holden develops this sense that he is supposed to be a protector of innocent young people. His imagined destiny as a catcher in the rye is juxtaposed by his true impact on his little sister. He drags his horrible habits of smoking and drunkenness into her room late at night. He is unable to think of the impact of his constant swearing and reckless behavior on her. She seems wise beyond her years but we are taking Holden's view on this and perhaps she is overwhelmed by what goes on around her.