To me getting in the Zone is not about technical training, or effort, or certain stimulus. I think the hardest thing about getting in the zone is that it is effortless. We (western society) are not a culture of "beings", we are a culture of "doings". Being in the zone is just that "being". What you do while in the zone is everything other people on this list have talked about accomplishing. I do believe that you can condition yourself to enter the zone. On the occasions when I have been in the zone I have never felt exhausted at the end. On the contrary I have usually felt like I had not expended any effort. That is assuming a sedate "zone" versus a competition zone.