One thing I like about running 100 miles is how it changed my perspective. I mean, of course, the idea of running 100 miles, since I haven't run that yet.
But even without having run it, the way I perceive distances has changed, radically, yet almost without me noticing when it happened. Before I ran my first marathon, a marathon was this incredible distance that I hoped to cover somehow, crawling if need be. Far out there. When I started training for a 50, a marathon became... duuuh, the halfway point. Now, thinking about a 100, marathons - I read this on a bumper sticker - are cute. A 50 is a warm-up run.
The body might think differently about this. But the mind, the mind has already adapted.