In my economics work, I have often heard of the Law of Unintended Consequences, defined by Tyler Cowen as follows:
When a simple system tries to regulate a complex system you often get unintended consequences.
A few weeks ago, my wife gave our three-year-old son an incentive: every time he poops in the potty, he gets to watch a few minutes of a dvd of his choice. He really likes watching and we severely limit him, so this seemed like it might work.
The next morning, I get up early with him while my wife and the baby try to sleep a little longer. Shortly thereafter I hear loud grunts and groans coming from the bathroom. I rush in to find our son sitting on the toilet, trying to make poop out of nothing at all, just so he can watch a few choice scenes of Thomas the Tank Engine.
We have since revised the incentive scheme. Some.