Jared Diamond in The New York Times:
You see, falls are a common cause of death in older people like me. (I’m 75.) Among my wife’s and my circle of close friends over the age of 70, one became crippled for life, one broke a shoulder and one broke a leg in falls on the sidewalk. One fell down the stairs, and another may not survive a recent fall. “Really!” you may object. “What’s my risk of falling in the shower? One in a thousand?” My answer: Perhaps, but that’s not nearly good enough. Life expectancy for a healthy American man of my age is about 90. (That’s not to be confused with American male life expectancy at birth, only about 78.) If I’m to achieve my statistical quota of 15 more years of life, that means about 15 times 365, or 5,475, more showers. But if I were so careless that my risk of slipping in the shower each time were as high as 1 in 1,000, I’d die or become crippled about five times before reaching my life expectancy. I have to reduce my risk of shower accidents to much, much less than 1 in 5,475. This calculation illustrates the biggest single lesson that I’ve learned from 50 years of field work on the island of New Guinea: the importance of being attentive to hazards that carry a low risk each time but are encountered frequently.
I first became aware of the New Guineans’ attitude toward risk on a trip into a forest when I proposed pitching our tents under a tall and beautiful tree. To my surprise, my New Guinea friends absolutely refused. They explained that the tree was dead and might fall on us. Yes, I had to agree, it was indeed dead. But I objected that it was so solid that it would be standing for many years. The New Guineans were unswayed, opting instead to sleep in the open without a tent. I thought that their fears were greatly exaggerated, verging on paranoia. In the following years, though, I came to realize that every night that I camped in a New Guinea forest, I heard a tree falling. And when I did a frequency/risk calculation, I understood their point of view. Consider: If you’re a New Guinean living in the forest, and if you adopt the bad habit of sleeping under dead trees whose odds of falling on you that particular night are only 1 in 1,000, you’ll be dead within a few years. In fact, my wife was nearly killed by a falling tree last year, and I’ve survived numerous nearly fatal situations in New Guinea.