In extreme weather, the weather is what is testing your mental fortitude. In many such situations you can’t “just quit” once you have entered the conditions, ot

In extreme weather, the weather is what is testing your mental fortitude. In many such situations you can’t “just quit” once you have entered the conditions, other than essentially committing suicide by ceasing to protect yourself. You can’t turn off the weather and go home just because you’re unhappy. In running, it is your own body that is testing your mental fortitude. To be more specific, it is the extreme physical discomfort one experiences while training and competing. And unlike life-or-death extreme weather, you really can quit at any point. It is a totally optional activity at all times. So yes, it requires quite a lot of mental fortitude to keep doing something so physically unpleasant, every day, in pursuit of a personal goal.