What foreshadowing in the book leads the reader to believe the descent was the most dangerous part of the climb in "Into Thin Air"?

From the text, foreshadowing:

And then these men did something remarkable. After a brief discussion, they turned their back on the summit and headed down the mountain with the assistant Sherpas. Earlier, Fischbeck, one of Hall's strongest clients, had also turned around. Why? The decision must have been supremely difficult for at least some of these men, especially Fischbeck, for whom this was a fourth attempt on Everest. They'd each spent as much as $70,000 to be up here and had endured weeks of misery. All were hard driving businessmen, unaccustomed to losing and even less to quitting. And yet, faced with a tough decision, they made the cool and reasoned decision that it was too late to reach the top and safely descend. They were among the few who made the decision. Unlike some less experienced climbers on that terrible day, they descended to safety, disappointed but alive.