Mind & EverydayFact
Pay someone to draw, and afterwards they draw less.
Lepper, Greene and Nisbett showed in 1973 that children given an announced reward for voluntary drawing later drew less on their own. The 1999 meta-analysis by Deci, Koestner and Ryan confirms the effect, but mainly for rewards experienced as controlling.
Useful: Reward work with information and recognition, not announced prizes for things people already enjoy.
Source: en.wikipedia.org