A lot of my crashes could have been avoided, it was just my own stupidity bar about 2 times, but even then if I was going slower for the unexpected it possibly may have not happened. I see a lot of crashes and nearly crashes from people lacking skills, they'll spend 5k+ on a bike then nill on learning how to ride it, knowing when you're fatigued and to back off is another contributor. I learnt the hard way years ago trying to ride above my pay grade on Moto's and my outlook today is to ride well with in my ability and to survive another day on the bike. I respect people that want to race but I feel like I've got nothing to prove at almost 50 other than to end up with broken bones, so I take it easy on my rides and if I feel like going fast on good days I just do, no pressure to perform, and it's a more pleasurable ride. Furthermore, I don't really ride for the competing factor, I just like getting out on the trails most days.
Two years after I got back into mountain biking, there was a young lad from WA that came over here to the east to study engineering, he took up mountain biking, came off on a water bar and unfortunately broke his back that caused him to be confined to a wheelchair. A few of us chipped in to help him buy a quad mountain bike powered by hands, he is still getting around AFAIK from state to state and started a support group for others in the same position to get into mountain biking.
Since then there's been another few bad crashes on the same set of water bars as they kick your back wheel up and the fire road drops away fast, so it puts most people on their front wheel and the next water bar flips them, but it's a reminder how things can go wrong so easily.