You’re running a day care center that closes at 5pm. You notice a handful of parents pick up their children late. Every time a parent arrives late it impacts you: you must stay late—family dinners and events are lost. What do you do? Realizing that your honor system isn’t cutting it, you start charging a fine for arriving late.
And then the unexpected happens: the number of late-arriving parents doubles.
This experiment was run by economists trying to help an Israeli daycare. The results confounded the researchers.