I've got to say I was one of those that said "it would never happen to me" but was I wrong. About 10 years ago I was hunting by myself in Central Texas and during a drizzling rain, I climbed up my single pole ladder to a hang-on stand some 15' above the ground. As I transferred from the ladder to the stand my rubber boot slipped on the wet stand and I lost my balance instantly. Like slow motion, I fell (not wearing a harness) and my hip hit the ladder on the way down. Fortunately, my Military training took over and I knew to roll when I touched down. Only by God's grace did I come out of this fall with only a twisted ankle.
When I hit, I did not know whether or not anything was broken but I laid there for a couple of minutes in the mud wondering if I had broken my back. I started to gently move my toes, then my feet (left ankle was hurting), then my knees. After moving my limbs, I sat up and didn't feel and discomfort other than the twisted ankle. I then proceeded to climb back into the stand (probably shouldn't have) but with much more care than the first time.
This fall taught me a valuable lesson...Use a Harness!!! I was one of the lucky ones. Be safe.