Experience was mentioned in the comments, but one thing that is missing is emphasizing the value of the subconscious brain(System 1 in Kahneman terminology). A lot of things experts "know" they cant verbalize. Consider a chess master, through thousands of games he has internalized a lot of patterns and "intuitively" knows what moves to consider. He doesnt have to be particularly rational in his thinking or practicing of chess, just sheer repetition is what gave him the skills.

The real power is in the brain(System 1) automatically picking up the patterns without we being aware of it.