Well I'm recovering from a bruised arse and a badly wrenched back (the painful bit!) from completely overcooking a manual at Parkwood Springs (the shame of it!), and dumping myself onto my fundament at 20mph.
The rule of thumb, is that it's always the stupid ones that do the most damage. Stuff like that above, "taking it easy" - that cost me a broken wrist on my first run of an Alpine holiday. If I'd been riding flat out, I'd have jumped the root that had me off. As it was I was bimbling, which meant I wasn't fully focussed on what I'm doing.
And that I think is the key. Focus. Commit everything, mentally and physically to the process of riding the bike. You're less likely to make mistakes when you're absolutely on it, and you'll spot them earlier, when you're concentrating on your riding, than being distracted by the pretty view, or the big scary rock off to the side of the trail. Night riding is a good example - there's nothing to see apart from the bit your lights illuminate, so you can clear stuff that you then can't do in the day time. Too much extraneous information distracting you from what you should be concentrating on.
My other half (who rides a lot slower/more carefully than me) often gets to the bottom of something and says "did you see XYZ?" or "where does that other trail go?", and I'm completely at a loss. All I've been aware of is the volume of space needed to get me & the bike down the hill - anything else is extraneous.