On May 17, 2016 the Albuquerque Journal reported the death of a hiker who had disappeared the previous December, on the Continental Divide Trail between Cumbres Pass and Abiquiu. Hikers found the body in a campground about 10,000 feet above sea level, east of Chama. The apparent cause of death was exposure. The hiker was experienced and had previously completed the CDT as well as the Appalachian and Pacific Crest Trails.
Like many such stories, this one may help us protect ourselves from a similar fate. Specifically, we can ask: how does a hiker with that much experience die of exposure? In response I'll indicate one possible decision and one obvious decision that, between them, may have eliminated the hiker's margin of safety.
First, the possible decision. The obvious way to die of exposure is to not carry enough gear to stay warm and dry, no matter what the weather brings. Some ultralighters instead advocate carrying just enough gear for the usual range of conditions. It's a gamble that works until it doesn't.
Second, the obvious decision: the hiker opted to be alone, at a time of year when, on that trail, even occasional encounters with other hikers were unlikely. There are dozens of ways another person can save your bacon, including having someone to care for you when you're injured, or lending you a layer when all of yours are soaked through, or lighting a fire after you lost your Bic in the snow.
Also, one effect of hypothermia is loss of judgment; in the early stages, when hypothermia is easiest to counteract, you may fail to recognize the need for remedial action. That other person can notice your daze and push you to take the life-saving step (such as starting a fire or getting into your sleeping bag) that your brain is ignoring.
Ideally, that other person is a hiking partner but if you must hike alone, doing so on a well-traveled trail at least gives you a chance of being helped when you need it.
I know, I know, people hike alone all the time. But that, too, is a gamble that works until it doesn't.