Anna Karenina Principle for 100 Milers

The Anna Karenina principle describes an endeavor in which a deficiency in any one of a number of factors dooms it to failure.

The Anna Karenina principle for running 100 milers:
100 Mile Finishers are all alike; every DNF is different in its own way.

6 reasons why runners (including myself) fail at 100s:

1. Nutrition - You need to eat (and keep down) enough calories, water, and salt to make it through 100 miles of running. That's ~200-300 calories per hour. It’s an all-day eating contest.
2. Pacing - You need to be able to sustain an effort that can last 100 miles while ingesting enough calories. Are you going out too fast? Yep!
3. Training - You need to put in enough miles/hours to be physically/mentally prepared to run 100 miles. But not so many miles that you burn yourself out in training. Everyone is different.
4. Equipment - You need to have protection against the extreme elements: cold, heat, rain, snow, lightning, hail, etc. Did you bring protection with you and make it available to you at key points in the race?
5. Injury - You need to stay safe in training and during the race. You've already won most of the battle if you get to the starting line healthy. 
6. Will to Finish - You need to want it badly enough to endure the very lowest points during the race. How much do you want it?

A successful endeavor (subject to this principle) is one where every possible deficiency has been avoided.

The name of the principle derives from Leo Tolstoy's book Anna Karenina, which begins:
“Happy families are all alike; every unhappy family is unhappy in its own way.”