Goodhart's Law

When a measure becomes a target, it ceases to be a good measure'. Universities optimise for grades instead of knowledge. Politicians seek popularity, not the public good. Tomatoes are bred into heavy, flavorless sacks of water. Soviet Nail factories, when instructed to produce a certain number of nails per month, produced tiny, useless nails.

from "Tiny Nails"

Quoted on Sat Jun 8th, 2013