"A man's gotta know his limitations".

That said, everyone's abilities are finite, and in a relative sense, there's not that much difference. Whether you can go 50 miles in a day or only 5 probably won't make a lot of difference in those situations where running like hell is going to apply. I realized in Baghdad that being able to run 100 meters faster than anyone else around me was more important than the next 900. In other circumstances, I would expect endurance might be more important than speed, so I try to maintain both to some degree, but at 47 I am no longer what I'd consider an athlete. My knees won't take the beating, my cardio just won't keep up like it used to, and even my reflexes have noticably slowed. I've tried to rationalize that I've replaced some of that reaction ability with reason and experience.

In the big scheme of things, I find that there are few incidents where a fit person would "just make it", and a less conditioned person has no chance. You likely won't fail unless you quit, pace isn't as much a factor as we would prefer.

I would like to be in better shape than I am. I would also like to be a better shot, a better driver, a better cook, but all these things take time, and I am kinda busy just trying to live life so I do what I can and leave the rest to those with more time on their hands. I am not at the frontline fighting a war, and there's little chance I ever would be again. I can get home on foot from most places I frequent and have good plans in place for making sure the risks are minimized if I have to under duress. Beyond that, I maintain a suitable condition to pursue what pastimes I can afford.