It's not the fall that hurts, its the sudden stoppage.
I generally go into races with a few goals in mind. They generally surround finishing, a time or pacing, and running smart. But I forgot to mention one: don't fall. Or if you like positive thinking, keep the rubber-side down. (The latter is an HBE reference: Todd told us to keep the open side up.)
I have run in eight ultras, finished six of them, and fallen in five of the six I've finished. Quick math: I've finished one ultra in which I haven't fallen. I can't remember whether I fell in the two I DNF's from, and frankly, I don't care.
And falls hurt - at Sawtooth, I felt like I could have broken a finger. At Superior 50K 2011, I sprained my ankle for a second time in the same race due to a fall. At Afton Alps, I could have slid down a ski hill when I foolishly stepped on a tuft of grass instead of the dirt trail while rounding a hill. At Surf the Murph 2010, I fell into the mud and came up a mess. End result: the consequences of falling may one day put me in the same crowd as Tony Krupicka's 2011 season - hobbled and rehabbing for several months all while blowing up the remainder of the season (and maybe part of the next). So it's best to avoid that whole falling thing.
So many things come together to ensure that you keep your soles facing down - foot placement; footwear; roots, rocks, and ruts; terrain; speed; level of exhaustion; etc. I fell once at Sawtooth when I got cocky, and almost fell several other times when I hit the aforementioned roots, rocks, and ruts.
This year I won't fall. I will run smart, place my feet well, and take three steps when I could take one or two.
You watch me. I won' fall, despite the miles and the surfaces and my choice of footwear (I'm wearing sandals at Afton, you just wait.)
(h/t Meghan Hicks)