The overjustification effect, also known as the overreward effect, is a psychological phenomenon that affects an individual's intrinsic motivation. This effect occurs when someone receives an external reward or incentive for performing an action that is already intrinsically motivated. The paradox here is that intrinsic motivation can decrease as soon as external rewards come into play.

In simpler terms, this means that if someone enjoys doing a task or activity because it is fun or provides personal satisfaction, and then is suddenly rewarded for performing that task, the original pleasure or motivation may diminish. This happens because the person begins to see the external reward as the main reason for the action, rather than the internal pleasure of doing it.

The overjustification effect has far-reaching implications, particularly in educational and professional contexts. For example, over-rewarding students for reading books could lead to them being less intrinsically motivated to do so of their own accord. Similarly, financial incentives in organisations could lead to employees doing their work less out of passion and more because of the rewards.

Research on this phenomenon shows that it is important to find the balance between extrinsic and intrinsic motivation in order to maintain long-term motivation and performance. It is about fostering intrinsic motivation while providing appropriate external incentives without undermining the intrinsic enjoyment of an activity.

Overall, the Overjustification Effect highlights the subtle dynamic between external rewards and internal motivation. It is a fascinating concept in psychology that deepens our understanding of how people are motivated and how to maintain that motivation.