One of the themes that comes up in the final chapter "The Lives of the Dead" is the idea of fact and fiction and the power of stories. O'Brien writes repeatedly about Linda, the girl he loved as a young boy, and who died when he was nine. In various situations, in his dreams, in his nightmares, and in his mind he can bring her back to life, and those visions seem as real as the reality he sees in his waking hours at times. He ends the chapter (and the book) with the idea that he is trying to save Linda with a story and he may very well be trying to save himself with a story. The idea of a story being uniquely powerful and useful, despite it being fictional, fills the last chapter.
Another theme appears in the second to last chapter, "Night Life." In it, Rat finally loses his "cool." The limits of the human mind and spirit and how much fear and darkness it can take are explored as the platoon moves only at night in the creepiest of circumstances and the strain is palpable. Eventually Rat loses it and shoots himself in the foot in order to get out, O'Brien carefully examines the limits of human endurance in the chapter.