The internal conflict driving the story is one based in guilt: Dunstan feels responsible for Mrs. Dempster’s premature labor (since the snowball that hit her was meant for him). This guilt compounds over the course of the story: subsequent misfortunes also seem linked to Dunstan’s behavior. He is banished from the Dempster’s house for teaching Paul magic (something to which Mr. Dempster is religiously opposed). He is the one that discovers Mrs. Dempster with the tramp, leading to her imprisonment by her husband. In fact, everything he does seems to have some kind of tangential effect on the life of Mrs. Dempster, who eventually goes insane and dies after spending most of her life in a mental hospital. Conversely, Dunstan begins to think of his own hardships as sacrifices he’s made to atone for his guilt. He believes in some ways that his leg—lost during the war—is a kind of cosmic punishment for his role in the unlucky accident involving Mrs. Dempster.
Another major tension in the novel concerns the fact that Boy Staunton, who actually threw the snowball that hit Mrs. Dempster, feels no guilt at all. In fact, it is revealed at the end of the story that Boy has completely forgotten about the Dempsters' entire existence. Boy still is forced to make a sacrifice in atonement, however—Paul Dempster eventually kills Boy Staunton after Dunstan confronts Boy about his role in Paul’s life. This death is rendered directly symbolic by the fact that Paul places the stone that was in the snowball (which Dunstan has kept) in Boy’s mouth the night of his death.
Much of the fortune and misfortune in the novel is framed by Dunstan’s letter as a kind of cosmic back-and-forth between guilt and sacrifice, wrongdoing and atonement. The book therefore offers a way for the reader to understand how we sometimes cope with or comprehend tragedy. The novel spans two world wars and the Great Depression, events that were characterized by irrational—in fact incomprehensible—loss and degradation. Accordingly, the book’s discussion of guilt can be read as an explanation of how its narrator learned to rationalize the irrational. Perhaps it should not come as a surprise that Dunstan is so quick to attribute a kind of significance to every loss and hardship, when so much of his life and others’ seems to be defined by such hardship. Guilt is not simply a psychological phenomenon in this book—it is historically meaningful. (This theme is closely tied to the themes of “History and Mythology” and “Love, Family, and Psychology.)