Quote by W. Edwards Deming
A numerical goal leads to distortion and faking, especially when the system is not capable of meeting the goal. Anybody will meet the quota (goal) allotted to him. He is not responsible for the losses so generated.
Blog posts exploring this idea: Achieving the goal by not the aim, The Trouble with Incentives: They Work, Distorting the System, Distorting the Data or Improving the System
Book: The New Economics