Traditionally, when psychologists and laypeople alike have talked about motivation, they have usually referred to the amount of motivation someone has (or doesn't have). “How can I get my child more motivated to do schoolwork?” or “How can I get my employees more motivated to do their jobs?” someone might ask. The implication, of course, is that more motivation would make the child do more schoolwork and make the employees work harder at their jobs.
It makes sense that if these individuals have more motivation, the child would do more schoolwork and the employees would do more work. However, having more motivation would not necessarily lead them to do high-quality work. When I think about motivated behavior, I am generally interested in seeing high-quality behavior rather than just a large quantity of behavior.
Take learning, for example: One person who is highly motivated to learn might spend time memorizing facts, whereas another who is highly motivated might spend time learning concepts and themes that tie facts together. In general, I find the second type of learning preferable, but if all you know is the amount of motivation a person has for learning, you would not be able to predict whether the learning would be the lower-quality learning (viz., memorization) or the higher-quality learning (viz., conceptual understanding).
When I was a graduate student, it occurred to me that predicting the quality of learning (or playing basketball, or managing a company, or solving problems) would require differentiating the concept of motivation into types of motivation rather than just focusing on the amount of motivation. In other words, I thought that some types of motivation might lead to higher-quality behavior than other types. I also thought that perhaps the high-quality behavior would be accompanied by greater well-being.
At about that time I became captivated by the concepts of intrinsic motivation and extrinsic motivation, which very few people were writing about back then. I knew immediately that that was what I wanted to research. The concept of intrinsic motivation, which means doing an activity because it is interesting and enjoyable, resonated deeply within me, and when I looked at young children playing, I knew I was watching a beautiful example of intrinsic motivation.