In The Outsiders, sunrise and sunset are symbols of unity and connection. For example, when Ponyboy connects with Cherry at the movies on the topic of sunsets, he begins to realize that all humans are linked through the natural world.
Finally, the book ends using the exact words that it began with. This is a symbol of the journey that Ponyboy has been on. It shows that he was able to work through all of the destruction that occurred throughout the story. It provides symmetry in the novel as well.
