There are several reasons I am a skeptic of accounts of willpower from elite military sources:
* Military life has social aspects -- like powerful authorities and close knit teams -- that may affect willpower. Advice on improving your own willpower often includes accountability techniques with other people.
* More on social effects: anecdotes from soldiers include transcendent experiences of groups bonding over common survival interests and outgroup hostility. The kind of cohesion experienced by a platoon stranded in a hostile Afghanistan valley probably isn't possible in your Weight Watchers group.
* More generally, note that a military is an organization whose success relies on convincing people to act against their own interests. I assume they have plenty of tricks they use to modify soldier behavior. That doesn't mean those tricks will translate easily for us civilians.
* People that make it onto elite military teams probably already have abnormally high willpower. Just because Michael Jordan says it's easy to dunk a basketball doesn't mean it will be easy for you to dunk a basketball. It just means Michael Jordan is an outlier.
* Publication bias (of a sort) and/or lying. Who wants to be the Navy SEAL that says, "yeah there's a point at which I wimp out just like normal people"? Such a person would be tempted to keep their mouth shut or lie about their opinion.