In 1973, psychologists Mark Lepper, David Greene, and Richard Nisbett ran an experiment with nursery school children who enjoyed drawing. Some children were promised a reward for drawing; others were not. Later, when drawing materials were made available without any reward, the children who had been rewarded drew significantly less than those who hadn't. Adding a reward to an activity they enjoyed had made them enjoy it less.
This phenomenon — the "overjustification effect" — is one of the most robust and counterintuitive findings in motivational psychology. It has been replicated dozens of times, with different activities, populations, and reward structures. It challenges the intuitive assumption that more incentive always means more motivation.
Intrinsic and extrinsic motivation
Psychologists distinguish between intrinsic motivation — doing something because it is inherently interesting, enjoyable, or meaningful — and extrinsic motivation — doing something for an external reward or to avoid punishment. Both can drive behaviour. But they work differently, and mixing them can be destructive.
When you do something for intrinsic reasons, you attribute your behaviour to genuine interest. When you add an external reward, your brain has a new explanation available: "I'm doing this for the reward." The internal motivation doesn't simply add to the external one — the external one can crowd out the internal one. The activity starts to feel like work rather than play.
The reward doesn't add to the motivation. It can replace it — leaving nothing when the reward is removed.
When extrinsic rewards help
The picture is more nuanced than "rewards are bad." Research by Edward Deci and Richard Ryan — who developed Self-Determination Theory, the leading framework in this area — shows that the type of reward matters:
- Tangible, expected rewards for interesting tasks consistently undermine intrinsic motivation.
- Verbal rewards and feedback that are informational ("you did that really well") can enhance intrinsic motivation by providing competence information.
- Unexpected rewards after a task have less negative effect, since behaviour during the task cannot be attributed to the reward.
- Rewards for uninteresting tasks don't undermine intrinsic motivation — there's little intrinsic motivation to undermine.
The autonomy dimension
Self-Determination Theory proposes that intrinsic motivation depends on three psychological needs: autonomy (feeling that you are choosing to do something), competence (feeling effective), and relatedness (feeling connected to others). Extrinsic rewards undermine autonomy — they shift the perceived locus of causality from internal to external. The activity that felt chosen starts to feel controlled.
The practical implication: If you want someone to develop genuine long-term engagement with an activity — a child learning to read, an employee developing a skill — use rewards carefully. Provide feedback on competence, support autonomy, and be cautious about using tangible incentives for activities where you want the person to develop intrinsic interest.