I FACED A SHEET OF ICE, which stretched from the tips of my boots into the clouds above. I hooked into the same nylon climbing cord as my younger brother, Rob, who stood 10 feet in front of me. He was staring up at the Jamapa glacier as he doled out advice. "Just do what feels right up there," he told me.

Rob's optimism had been guiding us since we'd begun this climb two days ago. We were 16,000 feet above sea level and physically unscathed; though we'd had a few spats, his intuitive approach proved to be the right...