Last April I went on an astronomy-oriented trip to Iceland. On our very first night going out to look for the aurora borealis, several of us hiked up a truly puny hill to get a better view of the northern horizon. The thing couldn't have been more than 10-15' high, with a gentle slope - but it was composed entirely of volcanic ash and loose pumice. Very unstable footing. On my way back down the hill, I slipped and landed on one knee in a sort of lunge position, fortunately unhurt, and I thought to myself "I didn't know the footing was going to be so tricky, I should have brought my trekking poles!" After I made it down to the base of the hill, I heard someone behind me cry out, and turned around to see another woman sitting on her butt halfway down the slope, with both her legs sticking straight out in front of her. At first I thought she'd just slipped and needed some help getting back onto her feet again. Then I noticed the funny angle of her left foot...
The lady spent the rest of the tour week in a hospital in Reykjavik, where a team of orthopedic surgeons painstakingly pinned her completely shattered ankle back together again. One small slip ended her entire vacation.
Needless to say, I've got a LOT more respect for unstable footing now, and far more appreciation of just how quickly a person can go from sound and healthy to totally crippled if they twist a limb in just the right way as they go down. And I appreciate my poles even more!