What I like of mountain biking is that it requires physical effort as much as mental effort.
This is expecially true for more challenging disciplines as All Mountain (AM) and Freeride (FR), but to it is important for Cross Country (XC) as well.
Physical skills can be trained and the same is true for mental ones.

Have you ever been on a ride where you suck, crash a lot and can’t negotiate the simplest obstacle? That happens to me a lot and it is generally when my mind is somewhere else. The situation usually improves during the ride and I feel a lot better by the end of the ride. My mind is not where it is supposed to be, i.e. focusing on the trail and my front wheel and my pedal stroke.