What metaphors are used in Charlie St. Cloud: A Novel by Ben Sherwood?

Charlie's promise to Sam becomes a metaphor for the grief that often becomes all-encompassing for some people. Some people simply cannot let go of their dead loved one and move on with their lives. Charlie physically cannot move on with his life because of his promise to Sam. However, when Charlie breaks this promise, he frees both himself and Sam for bigger and better things. Again, this is a metaphor for letting go, for freeing oneself from grief and getting on with a good, happy life.