Well, the book actually ends a bit more positively. Your actions will indirectly affect others isn’t just about the bad. It’s also the good.

The protagonist was haunted since he fought in the Vietnam War. He was ordered to burn an abandoned village but he thought he saw a shadow. He tried to see if someone was there while his commander told him to leave. He went anyways but was shot in the leg.

For his entire life, he was haunted by that.

The final person he met was a little girl. She was the shadow he saw. He broke down about how he wished his life could have been taken instead but she comforted him. Because of his guilt and pain, he was extremely cautious at his job as an amusement park maintenance employee. He went above and beyond what anyone else would do.

She showed him examples. Kids who were playing on the boardwalk that would have died after stepping on a broken plank. Rides that would have crashed because of a missed problem. Teens who would have plunged to their death because no one yelled at them to stop leaning over the rails. Even the action that caused his death - he saved the life of a little girl who was about to be hit by a roller coaster car.

Your actions can indirectly lead to bad things happening but they can also directly or indirectly bring about good.