I think most endurance athletes have had this conversation with themselves once or twice. How did yours turn out?
As I have been free from training since the San Diego Marathon, due to rest then injury I have been doing a lot of thinking about training. My conclusion? Training for endurance events is equal parts training, diet, and mental preparation. The best athletes in any endurance event are strong mentally, even those who are mid pack contestants usually have a fairly strong mental make up. Is that to say that they never have off days? Of corse not. Everyone has heard or had days where they were not in it mentally but still pulled a PR out of the bag. Conversely I myself have had many, many training sessions and races where I thought I was fully prepared and mentally ready to eat the course up, and fell apart by the mid point.
Life, and everything in it is all about balance. My favorite post ever on letsrun.com is about balance in life. I luckily saved it as it is no longer on the boards, someday I will post it here.