The growth of a person's ability seems parallel to the growth of a weight lifter's strength. The obvious is both increase over time with experience in moving the 'weights'. The inobvious is that without changes in the vector of stimulation, human muscles will plateau in their development. The same seems to happen with any knowledge, in that after a while the gains of study and experience slow. Changing the vector of stimulation shocks these systems into 'adding new mass'. New experiences open new neural pathways and adds to one's ability to cross-reference to find older knowledge and to create new knowledge. Similarly, new movements, repetitions, sets, and weights break weak muscle fibers at different angles, forcing the muscles to repair and add new fibers in preparation to handle the new forces they are required to handle.
Another similarity is when more and more different skills are called into play to perform a movement. In WeightLifting? there are a few large movements used by professionals as the staple of WeightLifting? which include squats, deadlifts, and less so with bench presses. These movements insist that the lifter make use of multiple sets of muscles at a time, thus increasing the amount of energy and focus necessary to successfully and safely perform the movement. Because these actions are demanding upon the brain to coordinate these efforts, the brain benefits from this as well.
This same method applies to all learning. The more skills are called into play in order to successfully produce a given work or action, the more the brain must coordinate them through crossreferencing. Again, this crossreferencing opens new neural pathways and adds to one's ability to cross-reference to find older knowledge and to create new knowledge.
In point, an effective individual (or writer/programmer as argued in SpecializationIsForInsectsDiscussion) should be able to draw upon many different knowledges and pull them together into broad movements. This would allow that individual to gain far more knowledge and wisdom than a person who chose a few specialized knowledges: A writer would gain a vast array of knowledge from which to spawn new stories. A programmer would gain much more from learning many different aspects of programming as well as learning many different useful programming languages, all of which would yield far more efficient programs in less time. ...a fisherman would catch better fish... ...a parent would be more effective in teaching a child... in fact, this process is precisely why children learn so quickly.