At the risk of jinxing myself (I've never typed the word "jinxing" before, and I sorta like it!), I will make a dangerous observation: over the years I've come to realize that I'm quite surefooted on the trail. I rarely fall and have never--yet--had a spectacular fall in which I drew significant blood or caused significant injury.
Analysis? I think that years of trail running trains--in the sense of strengthens--the ligaments, tendons, muscles, and even the bones of the total leg. As a result, the foot, ankle, knee, and hip joints are more resilient to unevenness of footing and consequently more resistant to injury.
For example, during a trail run I sometimes roll an ankle on an uneven surface, swear involuntarily, hop about, wonder if I'm injured...then within 30 seconds I've resumed running as though nothing has happened.
I have had a couple of falls that were more funny than serious, and occurred when I least expected them--coming off a trail onto a "safe" surface. Once I had covered some 20 miles of the Appalachian Trail, only to take a header when I crossed a paved road. A similar fall occurred when I was running the JFK 50 Miler, where I left the towpath to cross the Antietam Aqueduct, and promptly caught a toe and tumbled to the ground right before entering the aid station.
In both cases, wounded pride, not a wounded body.