How Stupid is doing the right thing?

While working at a movie theater I came across a large wad of bills. It was on the floor in the very back and there was about $200.00. The other ushers wondered what to do. Seeing as how I was not 100% trusting of our night manager I put the dough in my pocket and went through various options I had available to me. It never occurred to me that the money was now my own. Mostly I kept thinking of how panicked I would be if I lost that much.

As we began closing for the night, I was still at a loss for how to handle the situation. A knock from the glass covered front drew our attention. There was a look of desperation that tagged him as the one. One of my co-workers, who was aware of my find, motioned me over. The man told us how he had lost a good sum of cash. My own mind wanted some additional confirmation so we let him in to "look" for the cash. His beeline to the exact seat was enough for me. So I produced the wad and he looked quite relieved. He peeled off a 20 and offered it to me. I declined

The discussion came up that the smart thing to do would be to pocket the money. The ethical spin being that it would teach the looser of the cash a valuable lesson.

This is perplexing on many levels.