A good article by Chip and Dan Heath on incentives. Here’s the first paragraph:
Ken O’Brien was an NFL quarterback in the 1980s and 1990s. Early in his career, he threw a lot of interceptions, so one clever team lawyer wrote a clause into O’Brien’s contract penalizing him for each one he threw. The incentive worked as intended: His interceptions plummeted. But that’s because he stopped throwing the ball.
(And for a bonus, you’ll also learn why the really cold upper-Midwestern winters don’t make the people here less happy overall.)