
Even if we knew every rule, however, we might not be able to understand why a particular move is made in the game, merely because it is too complicated and our minds are limited. If you play chess you must know that it is easy to learn all the rules, and yet it is often very hard to select the best move or to understand why a player moves as he does. So it is in nature, only much more so.
volume I; lecture 2, "Basic Physics"; section 2-1, "Introduction"; p. 2-1
The Feynman Lectures on Physics (1964)