There two kinds of endurance. Probably more but for the purposes of this they all fit into just two. The first is a rote mechanical defense against stress. Very basically the tensing of a muscle. It is reactionary and instantaneous. It comes naturally and some will fare better than others under a particular stress using this limited form of endurance. Each will eventually break. There is another kind of endurance which I believe is, if not limitless, far superior at coping with stress. This is one that does the opposite of flexing or flinching. It is the relaxation of the body as it navigates obstacles. A balance between control of and flexibility so efficient that the noticeable repercussions from navigating stimulus lie outside our common realm of experience. It grows out of confidence and experience. A calmness that allows you to stay in the moment and let fear and pain pass effortlessly from the mind. Like a person gracefully relaxed while running downhill who stays in an ideal place between complete control of the decent (stopping) and complete release (falling). This is a state where one relaxes and lets the ground come to them and flow past. They don't push off the ground so much as pass over it. They are converting the downward force of gravity into horizontal movement. You reach this form of mastery in any skill when you practice it to the point that the idea of it transcends the mind. You do it without actually thinking it. In endurance it takes a kind of emotion to relax the mind and body. This may come through discipline in training, meditation, or fostering a healthy mental attitude. Perhaps it requires all three. Both types of endurance are beneficial to explore and cultivate. You might call the first form STRENGTH and the second FLEXIBILITY. However they both increase your strength when defined as tools that help you navigate impediments.