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.
Most successes are unhappy. That's why they are successes - they have to reassure themselves about themselves by achieving something that the world will notice.
There will come a time when everybody will know why, for what purpose, there is all this suffering, and there will be no more mysteries. But now we must live ... we must work, just work!