This short 45 minute Bill Evans documentary, created in 1964, is very interesting.
"Its much more important, Evans feels, to master fundamentals, both in theory, so that you understand what you're doing, and then in active practice developing ones musical muscles. Not just technical facility but also the brain connection with the arm muscles so to speak, developing that facility to the point where the subconscious mind can take over the basic mechanical task of playing, thus freeing the conscious mind to concentrate on the spontaneous development that distinguishes the best jazz...
Universal Mind of Bill Evans (1966 Documentary) - YouTube