Climbing with oxygen for the first time in my life, I took a while to get used to it. Although the benefits of using gas at this altitude—24,000 feet—were genuine, they were hard to discern immediately. As I fought to catch my breath after moving past three climbers, the mask actually gave the illusion of asphyxiating me, so I tore it from my face—only to discover breathing was even harder without it.
