One stems from the fact that every mountaineer knows there is a good chance when he takes off at midnight that he or she won't do it. A million things can go wrong. You can get a cramp. You can fall off. You can get too cold and get frostbite.
Bad weather can move in.
It can get scary and you can lose your mountaineering drive. Even the great climbers. Once you get to the top, there is a tremendous sense of relief and then the objective is to get back down alive and then you can feel the emotions. But I was lucky. Reinhold Messner noted it was so cloudy and gray he could hardly see anything.