This quote touches on several themes--including alienation and guilt vs. innocence--which can be found throughout much of To Kill a Mockingbird. After young Arthur Radley's second scrape with the law--stabbing his father in the leg with scissors--Mr. Radley again agrees to get his son out of jail by keeping him sheltered within the Radley house. Jem assumes that the only way this could be done would be by chaining Boo to his bed, but Atticus comments that "there were other ways of making people into ghosts." Mr. Radley's forced home imprisonment need not be like a jail cell; Boo is probably watched closely by his parents to make sure that he never leaves the house, and the psychological pressure put upon his son gradually reduces him to a recluse. Boo's social life is eliminated; he has no friends, and he is probably reminded often of the mistakes he has made and how another one might send him to jail or, worse, to a mental institution. Boo may have been aware of the rumors spread about him--that he is some sort of monster and not fit to mix with the public--and, as Jem put it later in the novel, perhaps Boo "doesn't want to come out." Although most of the town is afraid of Boo, perhaps it is Boo who fears the town and most of the people in it (aside from Jem and Scout).