What event triggers the central conflict in "Fifth Business"?

The event that triggers the central conflict in "Fifth Business" is the snowball incident involving Dunstan Ramsay. This pivotal moment occurs when Dunstan, as a child, is struck by a snowball thrown by his schoolmate, causing him to feel a deep sense of guilt and responsibility for the injury of another child, leading to a tragic consequence. This incident not only shapes Dunstan's character and his lifelong sense of duty towards others but also sets in motion the complex relationships and conflicts that unfold throughout the narrative. The snowball incident serves as a catalyst for Dunstan’s exploration of themes such as guilt, responsibility, and the nature of saintliness, which are central to the novel.