Quillansculpture, same for me on how it happens so often. I suppose mostly it's unprepared people, who haven't read that much about the mountain before they attempt it. I'm the type that researches a hike or destination to the nth degree before I ever get on a plane. You probably are too. Before I ever set foot on the MMWT the first time, I felt that I knew virtually every step. Three books, several You Tube videos (Hike-Along Pete!), a bunch of map-study, and about a year on the WPSMB beforehand (particularly Steve, the resources that are now HERE).
Unfortunately, a lot of folks wing it. They think it's just a little tougher version of Baldy, or San Jacinto, or some other big local mountain they're familiar with. You go up, you come down, you drink beer. Some are exhausted and rattled, some are disoriented from hypoxia or AMS, and some are flapping their gums too much to notice the wrong turn they just made. I've been guilty of a number of missed junctions on trails over the years, especially in the west where blazes don't really exist, so I really do get the "oops" factor. What I don't get is continuing down the JMT for miles when the landscape is 180 degrees different than what you saw coming up. "Gee, I don't remember those big lakes. Or all those mountains that go on forever. Where's the Owens Valley? Funny - this looks like what I saw when I crested the ridge coming up." Night descents excepted, but no novice has any business trying to negotiate the upper reaches of Whitney after dark. For God's sake, Bob R, of all people, turned around just short of the summit last weekend due to impending darkness! Strict turnaround-time discipline has saved more lives than we can count. Conversely, summit fever has cost way too many. Also, I suppose for some the prospect of going back UP the JMT when you discover your mistake and are bone-weary is just too daunting. I think Wade Brunette's pack and ice axe on the west side illustrate some of that mindset.
