One day Brian's riding his bike with his friend Terry. They ride past a shopping mall, and as they do so, Brian catches sight of his mother sitting in a station wagon with a strange man doing things that a married woman really ought not to be doing. As is often the case with traumatic memories, this one manifests itself in minute, unerring detail. The narrator doesn't mince words when it comes to describing the effect that such a horrible memory has had on Brian:
THE MEMORY was like a knife cutting into him. Slicing deep into him with hate.
The secret of his mother's infidelity serves to highlight the traumatic effect that his parents' divorce has had upon him. Brian's isolation in the forest is symbolic of the loneliness he has felt since his parents split up. Also symbolic is the hatchet that Brian's mother gave him as a parting gift. She may have given him a truly horrible memory that haunts his dreams and waking hours, but she's also given him something useful, something that will help him to survive in the wilderness. The hatchet and all it represents gives Brian the chance to move on from the traumas of the past, to mature, and to assert his growing independence. The memory of his mother's infidelity has kept Brian in the past for too long, but the hatchet that she gave him also provides a means of escape from that past.