Goodhart's law

• Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.

(Goodhart's original 1975 formulation, reprinted on p. 116 in Goodhart 1981

1. Goodhart, Charles (1981). "Problems of Monetary Management: The U.K. Experience". Anthony S. Courakis (ed.), Inflation, Depression, and Economic Policy in the West (Rowman & Littlefield): 111-146.