A story I like to share that I believe is related to this:
I once solved a leap in a lucid dream.
In real life I practiced it for like a whole week, every day, repeating without mistakes, separate hands, everything, etc., I practiced it correctly, but when I got to play it I always got it wrong, I missed, and I didn't knew why because I did everything correctly. I thought (and I was probably right) that I made some kind of mental block myself.
Anyways, one night, during those days I was learning that piece, I didn't knew I was dreaming until I saw a piano, so I just sat and played that passage once and clean, then I woke up and went to my real piano and I played that passage complete and it was all solved... I've never missed that leap ever since I had that dream and I've never practiced it again. That's when I realized it's all mental, well, like 90% of it. The problem wasn't in my hands, it was inside my head. The real work is in the connection between your hands and your brain.
I've been trying to have a lucid dream again since that day, so I can practice in my sleep, but I've failed
