Step 1: Recalling the Text:
Douglas recounts this incident as the origin of a fear he carried into adulthood.
Step 2: The Incident:
Thrown suddenly into deep water by a larger boy, young Douglas experienced sheer terror as he sank repeatedly and struggled to breathe, and this brush with drowning became the root of his phobia.
Final Answer:
A prank by a bigger boy — throwing young Douglas into the deep end of a pool, where he nearly drowned — was the traumatic incident that instilled his lifelong fear of water.