The four key features that characterize Flow, or what 10000 hours of practice gets you

The first is an intense and focused absorption that makes you lose all sense of time. The second is what is known as autotelicity, the sense that the activity you are engaged in is rewarding for its own sake. The third is finding the "sweet spot", a feeling that your skills are perfectly matched to the task at hand, leaving you neither frustrated nor bored. And finally, flow is characterised by automaticity, the sense that "the piano is playing itself", for example.

via Zap your brain into the zone: Fast track to pure focus by Sally Adee, newscientist.com