Bob’s criticism of Jimmy is that he was not very ambitious or smart.
This story describes how two men agree to meet each other twenty years after their last meeting as childhood friends. A lot can happen in twenty years. In fact, the two men have gone down very different paths. Bob and Jimmy were good friends, but they have become very different people. Bob meets a policeman man walking along, who comments that he has done well. In return, Bob makes a comment about Jimmy where he explains why he doesn’t think his friend will have amounted to much.
I hope Jimmy has done half as well. He was a kind of plodder, though, good fellow as he was. I've had to compete with some of the sharpest wits going to get my pile.
The policeman makes an arrangement with another policeman to impersonate Bob and deliver a note. He was Bob the whole time. He just couldn’t bring himself to say it once he realized that his good friend Jimmy was a wanted criminal.
When you struck the match to light your cigar I saw it was the face of the man wanted in Chicago. Somehow I couldn't do it myself …
Jimmy is a plodder, but he is also a good person. He did not arrest Bob himself. His friendship with Bob means that much to him. His job as a policeman means more. That is why he had another policeman impersonate him. By the time Jimmy got wise and realized he was talking to an impersonator, and the first man he was talking to was actually Bob, it was too late.
This story demonstrates the irony of growing up. We sometimes find ourselves staying true to who our friends once were, and who we once were, rather than who they are now. Bob criticizes Jimmy for having no ambition, but it is Bob’s ambition that got him into trouble in the first place, and landed him in jail.