The Sorrow of War is in part a novel about memory. Kien believes it is his sacred duty to tell the story of the Vietnam War, but what he means is that he wants to tell the stories of the people affected by it. By doing so, he keeps them alive:

There was still too much to do. He had the burden of his generation, a debt to repay before dying. It would be tragic and unjust in the extreme if he were to pass away, to be buried deep in the wet earth, carrying with him the history of his generation (122).

Kien must finish his novel, because through the novel, and the memories he captures in it, his friends continue to live: “The personalities, both alive and dead, breathed and spoke to the author in his special world where everyone he had known still lived and walked and smiled and ate and joked and dreamed and loved” (109). 

The novel is built around memory. There is very little forward progress in it. Kien is around forty when he is writing it, and he is around forty when he finishes. The rest is memory: his days in the war; his days before the war, when he was happy; and his unhappiness after the war.