There are so many factors that can contribute to this scenario, it's difficult to put them all in a box, which is what most people try to do on Social Media. Doing a one day Pemi in the winter, means moving pretty fast and burning a lot of calories. Maybe he wasn't at the top of his game? (had a cold, tired) and his body just ran out of gas, that could put him in a state that hypothermia would clearly take advantage of. Most people in this forum get that, no need to dissect those factors, but my point is, a lot can happen on these long and fast hikes. I see ultra fast hikers pass me and my 25 lb pack and don't give it much of a thought, but their margin of error and mine are just not the same. Unlike most hikers, I have been caught out with just a daypack, I spent a night around 14k, temps in the 20's and I was injured. I had plenty of clothes and carry today pretty much what I had back then. No sleeping bag, no stove, no bivi. But, I am fit, know how to conserve energy and monitor my body. I have read and believe that people in survival situations either excel at it or they don't. Many stories of survival leave no rhyme or reason as to how they survived, I think it's will. Just for the record, I'm talking in generalizations here , I'm not second guessing or impugning this poor guy in any way at all. It's really a tragic event, but mountain climbing is inherently dangerous, something everyone needs to remember when they step off the pavement. Prayers for his family.