So picture this: You're a receptionist at a hotel. Someone says they found a lost wallet but they're in a hurry. They hand it to you. What would you do? And would that answer be different if it was empty or full of cash?

The experiment started small, with a research assistant turning in a few wallets with different amounts of money. Acting as a tourist he would walk up to the counter of a big public place, like a bank or a post office, and ask the employee to take care of it.

The researchers assumed that putting money in the wallet would make people less likely to return it, because the payoff would be bigger. But researchers saw the opposite. Lead researcher Alain Cohn said, "People were more likely to return a wallet when it contained a higher amount of money. At first, we almost couldn't believe it and tripled the amount of money in the wallet. But yet again we found the same puzzling finding.”

What's behind all this honesty? The researchers suggest two explanations.

The first reason is just basic altruism—the person who reports receiving a lost wallet might care about the feelings of the stranger who lost it. They would want to return their valuables.

The second reason has a lot to do with how people see themselves—most don't want to see themselves as a thief. The more money the wallet contains, the more people say that it would feel like stealing if they do not return the wallet.