Of course, it's difficult to know 100% for sure and I'll say that there was probably more than one factor.
That said, in the post-race analysis my coach did agree with me and even apologized to me for not suggesting a more conservative pace.
We agreed hydration and fueling didn't seem to be an issue. Mental toughness is more subjective but I didn't get to the point where that even came into play.
I even pulled back into a conservative mode halfway through and couldn't even run 8:30's, which should be nothing.
Basically, I hit the wall, but I was able to at least somewhat hang in until I hit the 20 mile mark.
My feeling is I was just on the wrong side of using up my glycogen stores (although a part me still finds it hard to believe less than ten seconds per mile can change everything).
I could have seen running something like 3:35 but to fall all the way off to 3:43, I don't get it. It doesn't make sense to me that there was no middle ground. If my pacing was off, I would have thought I still would have been able to get a lot closer to the end before I started to have problems.
I read Luke's article in the middle of training and it didn't really clarify for me one way or the other.