I think mental toughness has as much to do with motivation as anything else. People can be mentally tough in situations they WANT to be in, and they can be mentally tough in situations where they find themselves wanting to survive (that is a different phenomenon in my opinion), but the same person can be a major whiner if they aren't feeling motivated in some way to be where they are.

For example, my son will start whining about hiking before we even get out of the car, he hates it that much. But he will walk 10 miles in an amusement park one day, and at least another 10 the next day walking around a city (which he loves), and only occasionally mention his discomfort (which I know must be extreme because in this case my legs were tired too). If he is doing something he loves he can push past the pain (and he has a high tolerance), but if he isn't then you better have your earplugs in.

I think you will find that the people who are not "mentally tough" in the outdoors are that way because they don't really want to be there, and are there for reasons other than because they love the outdoors.

MNS