Goodhart's Law states " . . . when you attempt to pick a few easily defined metrics as proxy measures for the success of any plan or policy, you immediately distract or bait people into pursuing the metrics, rather than pursuing the success of the policy itself."
Better: as Andy Grove supposedly said, "For every goal you put in front of someone, you should also put in place a counter-goal to restrict gaming of the first goal."
Even better: economist Glen Whitman wrote:
With just an iota of economics training, most people catch on to the importance of incentives. "Aha! To get people to do what we want, all we have to do is reward the good stuff and punish the bad stuff!" Alas, the world is not so simple. People don't always respond to incentives in the ways you might predict. What distinguishes good economic thinking from bad is recognition of the subtle, creative, and often unforeseen ways that people respond to incentives. Ignoring the complex operation of incentives is a recipe for unintended consequences.