From Josh Waitzkin in The Art of Learning, and applicable to investing and just about everything else as well:
As I struggled for a more precise grasp of my own learning process, I was forced to retrace my steps and remember what had been internalized and forgotten. In both my chess and martial arts lives, there is a method of study that has been critical to my growth. I sometimes refer to it as the study of numbers to leave numbers, or form to leave form . A basic example of this process, which applies to any discipline, can easily be illustrated through chess: A chess student must initially become immersed in the fundamentals in order to have any potential to reach a high level of skill. He or she will learn the principles of endgame, middlegame, and opening play. Initially one or two critical themes will be considered at once, but over time the intuition learns to integrate more and more principles into a sense of flow. Eventually the foundation is so deeply internalized that it is no longer consciously considered, but is lived. This process continuously cycles along as deeper layers of the art are soaked in.
Very strong chess players will rarely speak of the fundamentals, but these beacons are the building blocks of their mastery. Similarly, a great pianist or violinist does not think about individual notes, but hits them all perfectly in a virtuoso performance. In fact, thinking about a “C” while playing Beethoven’s 5th Symphony could be a real hitch because the flow might be lost. The problem is that if you want to write an instructional chess book for beginners, you have to dig up all the stuff that is buried in your unconscious—I had this issue when I wrote my first book, Attacking Chess. In order to write for beginners, I had to break down my chess knowledge incrementally, whereas for years I had been cultivating a seamless integration of the critical information.
The same pattern can be seen when the art of learning is analyzed: themes can be internalized, lived by, and forgotten. I figured out how to learn efficiently in the brutally competitive world of chess, where a a moment without growth spells a front-row seat to rivals mercilessly passing you by. Then I intuitively applied my hard-earned lessons to the martial arts. I avoided the pitfalls and tempting divergences that a learner is confronted with, but I didn’t really think about them because the road map was deep inside me—just like the chess principles.
Related quote: "Just as civilization can progress only when it invents the method of invention, you can progress only when you learn the method of learning." -Charlie Munger