It depends on the story.
One of the things that you discover working with people is that their expectations tend to skew conversation and/or experiences.
I hike with large groups, small groups, friends, and SAR team members. All of these are different experiences. I have come to realize that putting expectations on other people is folly - expecting all SAR team members to be mentally tough is a dumb thing to do, expecting all my friends to be is also unrealistic, expecting people who just joined the hiking group who also make claims of having lots and lots of experience to know what they are doing and make reasonable choices for themselves as to miles and strenuous hikes is also unrealistic - the proof is in the results. People do not know what they can do, and sometimes, the person is me - some trips I am the weak one, simply because my body is not up to the task, for whatever reason.
After some thought I have to agree with bill and say that mental toughness can be present but really does not have a lot to do with backpacking, because it's more reasonable to say that one should know and respect one's own limits, which can be extremely variable - I don't have issues with elevation 99 times out of 100 and can generally drive to 10,000 feet and start hiking, for example. But I'm not going to really push myself up the trail hard if I'm having a difficult time, because I understand the risks, and even if it's a SAR I'm not going to really risk much - it does no one any good to have a second subject to evacuate after I've pushed myself beyond my limits. Part of my responsibility to the SAR team is knowing when to say "No, I can't go on this one."
It is unreasonable to expect someone who goes backpacking once a year to be up to the same level of someone who goes every month, as well. Factoring in that not every trip is a test of will or fitness, mental toughness has little to do with who I go with - sometimes you want to fish, so I go with fishermen and women. I don't need them to be able to hike 10 miles with 50 lbs on their back and not complain.
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzukihttp://hikeandbackpack.com