Children are interested in characters that are involved in action and decision making. Characters in children's literature can be people, animals, or inanimate objects and are incomplete without different types of protagonists. Characterization is also provided through picture book illustrations. Traditional folktales rely on stock characters and have optimistic endings to comment on life lessons. Stories from many cultures often focus on the lazy but tricky character. Realistic animal stories expect animal characters to behave like real animals, though writers may imagine their thoughts and feelings. Science fiction has developed more fully realized characters as the genre focuses on future histories and how characters change. Classics continue to be read across generations because of their real characters that join one reader to the next.