I once heard of a concert pianist who prepare for concerts by reading the scores. On the plane ride over to a particular concert, he will look at the score and think about how to approach the piece. When he arrives, he just plays. The practice happens all in his head.
How does he do it? How does he encounter some of the most difficult pieces in the piano repetoire and sight read it as though it were nothing?
My theory is that through his career, he’s played enough pieces to recognize patterns better than the rest of us. It’s like reading. When you start to learn to read, you piece out one letter at a time. Then eventually you start recognizing parts of words, you piece out “to+ge+ther.” With more practice, you start digesting whole words and even whole phrases. When you skim a paragraph, you are no longer thinking about individual syllables or letters, but digesting chunks of information at a time.
Most people playing piano never advance past the first two stages. When confronted with a new piece, they are still sounding out the music one note at a time. I think when professionals do it, they absorb the music in chunks. The patterns are ingrained after years of practice. The work is how to interpret these patterns in interesting ways.