"On February 12, 1995, a party of three seasoned backcountry skiers set out for a day on the pristine slopes of Utah's Wasatch Mountain Range. Steve Carruthers, 37 years old, was the most experienced of the group, though they were all skilled skiers and mountaineers. Carruthers had skied these hills many times, and was intimately familiar with the terrain. Their plan was to trek over the divide from Big Cottonwood Canyon to Porter Fork, the next canyon to the north.

Two hours out, they met another skiing party. A storm had dropped almost two feet of new snow on the range the day before, and the two groups stood together for about five minutes, chatting about the best routes through the mountains. A couple of skiers in the other party were a bit spooked by the foggy conditions, but they all decided that they would be okay if they chose a prudent route across the lower slopes. Carruthers' party broke trail through the sparse woods of Gobbler's Knob.

Within the hour, Carruthers was dead. As the skiers headed across a shallow, treed expanse, they triggered an avalanche. More than a hundred metric tons of snow roared down the mountainside at 50 miles an hour, blanketing the slope and pinning Carruthers against an aspen. The other party heard the avalanche and rushed to the rescue, but by the time they dug Carruthers out, he was unconscious. He never regained awareness.

The other two skiers in Carruthers' group survived, but they faced some serious criticism back home. What were they thinking? This pass was well known as avalanche terrain, and February was considered "high hazard" season. The chatter in the tight-knit skiing community was that Carruthers had been reckless, that despite his experience he had ignored obvious signs of danger and tempted fate.

None of this rang true to Ian McCammon. McCammon had known Carruthers for years and the two had been climbing buddies at one time. Sure, Carruthers may have been a risk-taker when he was younger, but he had matured. Just recently, while the two men were riding a local ski lift together, Curruthers had talked adoringly about his lovely wife Nancy and his four-year-old daughter, Lucia. His days of derring-do were over, he had told McCammon. It was time to settle down.

So what happened on that fateful afternoon? What skewed this experienced backcountry skier's judgment, that he would put himself and his party in harm's way? Did he perish in an avoidable accident? Saddened and perplexed by his friend's death, McCammon determined to figure out what went wrong.

McCammon is an experienced backcountry skier in his own right, and a wilderness instructor, but he is also a scientist. He has a Ph.D. in mechanical engineering, and as researcher at the University of Utah he once worked on robotics and aerospace systems for NASA and the defense department. He already knew snow science pretty well, so he began reading everything he could on the science of risk and decision making. He ended up studying the details of more than 700 deadly avalanches that took place between 1972 and 2003, to see if he could find any commonalities that might explain his friend's untimely death.

With the rigor of an engineer, he systematically categorized all the avalanches according to several factors well-known to backcountry skiers as risks: recent snowfall or windstorm, terrain features like cliffs and gullies, thawing and other signs of instability, and so forth. He computed an "exposure score" to rate the risk that preceded every accident.

Then he gathered as much information as he could on the skiers themselves, all 1355 of them: the make-up and dynamics of the skiing party, the expertise of the group leader as well as the others, plus anything that was known about the hours and minutes leading up to the fatal moment. Then he crunched all the data together.

His published results were intriguing. He found many patterns in the accidents, including several poor choices that should not have been made by experienced skiers. He concluded that these foolish decisions could be explained by six common thinking lapses, and he wrote up the work in a paper titled "Evidence of Heuristic Traps in Recreational Avalanche Accidents." The paper has become a staple of modern backcountry training, and has no doubt saved many lives.

Heuristics are cognitive rules of thumb, hard-wired mental shortcuts that everyone uses every day in routine decision making and judgment. The study of heuristics is one of the most robust areas of scientific research today, producing hundreds of academic articles a year, yet the concept is little known outside the labs and offices of academia. This book is an attempt to remedy that.

Heuristics are normally helpful-indeed they are crucial to getting through the myriad decisions we face every day without overthinking every choice. But they're imperfect, and often irrational. They can be traps, as they were in the frozen mountain pass where Carruthers perished. Much has been written in the past couple years about the wonders of the rapid, automatic human mind and gut-level decision making. And indeed the unconscious mind is a wonder. But it is also perilous. The shortcuts that allow us to navigate each day with ease are the same ones that can potentially trip us up in our ordinary judgments and choices, in everything from health to finance to romance.

Most of us are not back country skiers, and we will probably never face the exact choices that Carruthers and his friends faced at Gobbler's Knob. But just because the traps are not life-threatening does not mean they aren't life-changing. Here are a few of the heuristics that shaped the backcountry skiers' poor choices-and may be shaping yours in ways you don't even recognize. . . ."

This is a short excerpt from the Introduction to On Second Thought: Outsmarting Your Mind's Hard-Wired Habits. I go on to discuss several of the cognitive heuristics that contributed to this tragedy--the familiarity heuristic, the scarcity heuristic, the mimicry heuristic, the default heuristic. These heuristics and many others skew all of our judgments everyday, and while they may not always be life-threatening, they are often life-changing. In future posts, I will be discussing these heuristics in more detail.

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