Bob and Jimmy remained "friends" for twenty years only because they hadn't seen each other in all those twenty years. If Bob had stayed in New York City they would have drifted apart because they had different values and different interests. Bob wanted money and luxury, and he didn't care how he got it. Jimmy was sincere and honest. He wanted a useful life, and he was not interested in impressing others. Jimmy liked security and stability. Bob, who is evidently a con man, couldn't have security or stability because of the way of life he had chosen. People like him had to keep on the move.
Here are a few pertinent quotes about friendship:
Do not keep on with the mockery of friendship after the substance is gone--but part, while you can part friends. Bury the carcass of friendship: it is not worth embalming. -William Hazlitt
It’s no good trying to keep up old friendships. It’s painful for both sides. The fact is, one grows out of people, and the only thing is to face it. -Somerset Maugham
A relationship is like a shark: it has to constantly keep moving forward or it dies. And I’m afraid what we’ve got here is a dead shark. -Woody Allen
Most friendships do not last. People change. They grow in different directions. It is a mistake to describe Bob and Jimmy as "old friends." What they are is erstwhile friends. That is, their relationship is based on the fact that they used to be friends. If they had gotten together for dinner that night and if there was no question of Bob's being wanted by the police, Jimmy would have found that his feelings about the flashy, materialistic Bob were not the same as they had been twenty years earlier. Bob, for his part, would have had to admit to himself that his old friend Jimmy had turned out to be a crashing bore, a stick in the mud. After they had finished their dinner and shook hands, they might have both been privately deciding not to pursue the relationship any further after that night. These things happen all the time. They happen in marriages as well as in friendships.
One of the themes in “After Twenty Years” is that people will act according to their natures.
This story describes two friends who agree to meet in twenty years. After twenty years, they both keep their promise. However, they have both lived a lot in that twenty years. Ironically, one became a cop and the other became a criminal.
The two friends corresponded at first but then lost touch with each other. Jimmy became a cop, and Bob became a crook. When Jimmy first met up with Bob, he recognized him but did not tell Bob who he was. Jimmy was a good man. He was a cop, and nothing was more important to him. However, he was also a friend. He could not handle arresting Bob himself, so he pretended to be a stranger and then found a cop to arrest Bob.
Bob comments that twenty years is a long time, but not long enough to change a person’s personality. Jimmy’s friend, the cop who arrested Bob, responds.
"It sometimes changes a good man into a bad one…”
Jimmy left Bob a note explaining why he had done what he did. He felt pressure between the two opposing forces of his friendship and his duty. Each man acted according to his nature. Jimmy knew Bob was a criminal and would continue to be a criminal. Jimmy was a cop, and could not shake off his cop nature enough to look the other way. He also was a friend, and could not arrest Bob because of that. He found a compromise he could live with.