In his book Into Thin Air, the harrowing account of the ill-fated 1996 expeditions to Mount Everest, mountaineer Jon Krakauer recalls his sense of foreboding as he helicoptered into the Himalayas with an ad hoc team of amateurs.

“I attributed my growing unease to the fact that I’d never climbed as a member of such a large group — a group of complete strangers, no less,” he writes. “One climber’s actions can affect the welfare of the entire team. The consequences of a poorly tied knot, a stumble, a dislodged rock, or some other careless deed are as likely to be felt by the perpetrator’s colleagues as the perpetrator?.?.?.?I suspected that each of my team mates hoped as fervently as I that [Rob] Hall [their professional guide] had been careful to weed out clients of dubious ability, and would have the means to protect each of us from one another’s shortcomings.”

In fact, eight climbers died in one day — including Hall — when storms closed in on the many groups, from first-timers and “tourists” to hardened professionals, who were trying to make it to the summit and back.