What experience/event in the memoir has the biggest impact on Tim O’Brien

The event that had the biggest impact on Tim O'Brien was when he killed a young man.

Explanation:

'The Things They Carried' is a memoir written by Tim O'Brien about his life when he served as a soldier in the Vietnam War. In his memoir he shares his experiences of loss and guilt and fear.

The event that shocked O'Brien was when he killed a man. In chapters titled 'The Man I Killed' and 'Ambush' he expresses hhis feelings of guilt of killing a man and how he will confront his daughter Katherine, when she will once again ask if he has killed anyone. In chapter 'The Man I Killed', the readers are able to see shock and guilt that overtook O'Brien when he killed a man near My Khe village, with a grenade. He continuously look at the body of the young man in shock.