From Tim Gallwey's The Inner Game of Tennis:
Much has been written as of late about the creative zone - that strange space in which you lose all sense of self, in which you volunteer yourself to something outside of you.
"Man is a thinking reed but his great works are done when he is not calculating and thinking."
Athletes at peak performance witness this regularly. I think anyone with a desire to master anything has experienced it at some point. Maybe a lawyer has an out-of-body experience while making a closing argument; an engineer makes a crucial breakthrough and works for 12 hours straight; during a lesson a teacher becomes the conductor, and the classroom her orchestra.
Among the overeducated, there's a tendency to place too much emphasis on the conscious mind. Reason, logical thinking, and explicitly expounded theories take precedent.
As we see from master craftsmen and artists, though, good shit happens when you just let things happen. But these people didn't get to where they have through haphazard practice. They practiced deeply on specific things. They've eliminated unacceptable weaknesses; they've highlighted and solidified their unique strengths.
The key, then, is in how you design your moments of deliberate practice. Are you getting interrupted every 15 minutes? Then you'll never hit your zone.