"... experience has taught me that the physical and mental preparation of a piece of music can take you only so far: putting the piece away for a time, letting it rest while the mind and fingers are occupied with other things, often leads to more development than the actual, quantifiable work does. Time and time again, I've struggled with something - the shape of a phrase, the handling of a transition - in a work that is new to me, searched and searched for a solution that seemed organic, and found that nothing I tried sounded natural - nothing passed the "rightness" test. But then, after leaving the piece for a period of several months, sometimes really not even thinking about it all, the same passage has somehow, through some kind of osmosis, resolved itself, and no longer poses a question at all."
That passage, from Beethoven's Shadow by Jonathan Biss, harks back to some of the points raised in this post. I wonder how common an experience that is for writers, putting away the work for some time and coming back to find that the way ahead is magically clearly marked!