The story goes that a man was upset that his neighbor kids would always play on his lawn and damage it. So he decided to pay each child to play on his lawn. The surprised kids gladly accepted. After a few days the man told them that he could only afford to pay them half of the initial rate. The kids accepted this reduced rate but were less then enthusiastic. After a few more days the man cut his pay to almost nothing and the children were so upset that they left, vowing never to play on his lawn again unless he increased their pay. Problem solved.
i find such pay-for-performance stories really really interesting
the opposite example is the one about the daycare parents who were fined if they came late to pick up their children. once this rule went into place, parents would just pay the fine to show up late (it was better to pay and be late than to be on time!)