It is not just a person's physical constitution, their intellegence, their education, or even their social conditioning that enables them to withstand hardship. Much more significant is their inner development. And while some may be able to survive through sheer willpower, the ones who suffer the least are those who have a high degree of patience and courage in the face of adversity.
I was out in the combat engineers. We would throw up bridges in advance of the infantry but mainly we would just throw up.