I wear a full-face helmet on a mountain bike, too.
My point is that when mountain biking, you encounter varied terrain and obstacles and you decide how to approach that based on your skill and experience. Some approaches are riskier than others. And sometimes you decide the best thing to do is just nope out and ride or walk around whatever it is.
I don’t think there’s any riding situation where you can think you’re in complete control of the risk.