That goes so much deeper than enjoyment. Seven days a week. I don't walk away from the work. The snipers did everything they could to limit the incursion of the body. The body gets in the way of the accuracy of the rifle.
Writing is kind of the same thing.
So I stay in the best phyisical condition I can. When I was researching the book I'm on now, it was a very conservative research effort. Every day, seven days a week, at least eight hours a day. I kept a log to make sure I stayed on pace. I set myself a goal of reading at least two books a week.