Knew it, but can't do it.

[Bagger Lance]

Don't forget muscle "memory".
As another member posted recently, there is no such thing as muscle memory as muscles don't possess memory. It is the conditioning of the nervous system through repeated correct motions that builds and optimizes the nerve pathways to repeatable muscle actions.

So even though the concert pianist doesn't need to do physical practice in order to play on stage, its only because he has conditioned his arms, hands and fingers to respond to the notes and timing in his head...subconsciously.

As golfers, we need to practice doing the right movements over and over until the conditioning is automatic. Unfortuately, we can also program the wrong movements into our swing and overcoming those "engrained habits" with new habits takes a great deal of time and effort.