Last year, Malcolm Gladwell's book Outliers was based on the idea that success in a field comes from practicing tasks for ten thousand hours. This simplified meme provides a starting point for understanding Michael Jackson's success: when at age five one starts doing something constantly, utterly assured facility in that work through ten thousand hours of "practice" gets built up pretty early. Michael Jackson sang and danced so much so young that it became second nature. He may not have been able to read music (he composed by singing into a tape recorder), but he understood it on what is commonly called an intuitive level. In fact, what happens is that the more often one performs a task, the more neurons the brain devotes to that task, which increases speed and ease of performance until it becomes a reflex. That Jackson became an amazingly talented dancer and singer long before most other people do seems inevitable under these circumstances.
The flipside of this is a tendency to have the same reaction even when it may be less appropriate: as psychologist Abraham Maslow wrote in 1962, "When the only tool you have is a hammer, it is tempting to treat everything as if it were a nail." (This concept has become such a popular meme itself that the attribution to Maslow is usually forgotten; it has been so frequently repeated as to now seem to be folk wisdom.) This explains why successful creative people eventually repeat themselves and come to seem less imaginative; an exertion of will is required to overcome the reflex.
Tie this in with what psychologist Kenneth R. Hammond dubs coherence thinking. In correspondence thinking, perception is compared to physical reality; in coherence thinking, perception is filtered through a desire to be internally consistent, with a resultant inclination to assume that new events can be fitted into a system of logic shaped only by past experience and unconsciously assumed to always apply to all situations, to the degree that it actually alters the processing of perceptions.
Taking these ideas into consideration, the more one does something, the harder it is to stop doing it and do something new, to get out of a rut. No wonder Jackson, coming off the spectacular back-to-back successes of Off the Wall and Thriller, began sounding less original. Not only were many musicians copying what he and Jones were doing, Jackson and Jones were, in an entirely natural way, copying themselves.