Climbing at high altitudes
High altitudes aren't very good because they make you feel like crap and every step forward is difficult.
But those quintessentially goal focused individuals will drive themselves forward beyond pain to reach the summit.
Some will die in the attempt.
My own perspective is that mental goals (like reaching the top of a mountain) are not as important as physical health.
I will turn back or down once physical performance and comfort go below a certain level, hopefully way before one's life or limbs are threatened.