Reinhold Messner: The thin air makes, first of all, that you are becoming slower and slower. The higher we go, less pressure is in the air, so no more oxygen is coming to our energy in the blood. And the sugar in the blood is the energy.  We need oxygen to burn it, like to burn wood. If you go at 8,000 meters, you cannot make fire with wood. It’s not possible. There’s not any more burning. The oxygen is missing. And if there is not enough oxygen for your energy, which you have in your circulation of blood, you are doing one step and you do a rest, and another step and you do a longer rest, another step and the longer rest again. So you’re becoming infinite slowly.