The thing I find fascinating is the idea that when I say something like "I've run out of cope", it's not just a metaphor. There's some reality behind that.
And I think it's important to recognize the willpower tax of living under stress. I think we find it really hard to acknowledge just how contextual our decisions really are. We have this mythology of the self that says that people make choices as an expression of their inner nature, that good decisions come from moral fiber and inherent goodness, while bad decisions come from weakness and innate unworthiness, when in fact it's much much fuzzier than that. We say "oh, I would never make that choice," but in fact, in their shoes? You might. And that's scary, so instead of responding with compassion, we cast judgment as a way of distancing ourselves from the frightening reality that we don't have nearly as much control over our lives as we believe.
Also interesting is the point that people who manage decision fatigue well often do so not by having greater reserves of willpower, but by structuring their lives so they don't have to expend much of it under normal circumstances.
I think you could use that as a metric of civilization: the more a culture structures its context to allow its members to be the best they can, the better a civilization it is...