Knowing is Doing

From Knowing Is Doing, Not remembering:

My dad taught math. His most helpful lesson was that math skill is all about practicing the operations — no different than shooting a basketball. Comprehending long division, for example, isn’t so much a matter of memorizing the method, as it’s about a physical familiarity with making the right markings with a pencil on the paper: drawing the division symbol, plugging in your numbers, getting a new number and writing it below, digit beneath digit. By the time you’re exam-ready, the know-how resides in your bones and reflexes, not in your thoughts. Knowing is doing, not remembering.

I've found this to be true in my career and everyday life, particularly with computers and systems engineering. It's one thing to have a basic grasp of high-level concepts, and quite another to be able to accomplish a specific task without losing a bunch of time on looking up the details.

Also see how this relates to Chunking (psychology).