What significant event happened to Da in the List of Unspeakable Fears?

The significant event that happened to Da in "List of Unspeakable Fears" is that he died. This event is pivotal as it profoundly impacts the protagonist's emotional journey and the themes of loss and grief throughout the story. The death of a parent, especially in this context, serves to illustrate not only personal loss but also the broader implications of how such an event can alter one's perspective on life and choices. Da's death is a catalyst for the protagonist's reflections and fears, shaping the narrative's exploration of the complexities of family relationships and the inevitability of death.