I am glad you are bringing this up. It's impossible to cheat and skip training. I started running alpine trail (ultra) marathons three years ago, and every time I go for a >40km run in the Alps, the hammer of reality just comes down fast and hard on both mind and body.

In the beginning I have grand plans of finishing near the peak of the Gaussian distribution of my age group. After 10km I am cursing myself for not training more. After 20km I am just focusing on finishing, and after 30km on not dying.