Human behavior is often driven by some motivation. Social scientists have identified two types of motivation, extrinsic and intrinsic. Extrinsic motivation is some tangible reward for a positive behavior. Intrinsic motivation, on the other hand, is a self-propelled desire to gain some goal. One of the most fundamental forms of intrinsic motivation is the idea that the behavior is fun.
Internal rewards can be just as satisfying, if not more so, than some external token. For example, students entering college may pick a particular major because it interests them, and they wish to become better experts in this field. This is intrinsic motivation. Extrinsic motivation in such a case would be the promise of a high-paying job upon graduation, and little else. Individuals engage in intrinsic motivation when they attribute the desired results to factors that are under their own control, which psychologists call autonomy.
There are both advantages and disadvantages to intrinsic motivation. On the one hand, it can be long-lasting and self-sustaining. Most educational efforts are geared towards building intrinsic motivation within students. Systems of reward or punishment do not enter into the equation. Disadvantages include the notion that attempting to instill intrinsic motivation in individuals, such as students, can often be a long process. It is, of course, far easier to motivation people with a tangible reward, but perhaps less psychologically satisfying.