Does Trusting Your Instincts Make Sense?

A conversation on "heuristics" with Wray Herbert, author of the new book "On Second Thought."

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Think twice before you trust your gut, says Wray Herbert, author of the just-published On Second Thought: Outsmarting Your Mind's Hard-Wired Habits (Crown, $25). Herbert, director of science communication at the Association for Psychological Science and former health and science editor of U.S. News, uses real-world examples and cutting-edge research to show how heuristics—hardwired mental shortcuts we think of as intuition—can both help and hinder the decisions we make every day. The trick, he says, is knowing when and when not to follow our instincts. He shared his insights. Edited excerpts:

"Heuristics" is used throughout your book. Exactly what does it mean, and why use such an unfamiliar term?

I used the jargon "heuristics" in a popular psychology book because there really is no good synonym. Heuristics are mental habits that have been deep-wired into our brains and govern every decision that we make, from which brand of yogurt to buy at the grocery store to whom we decide to marry. Most of the heuristics I discuss have ancient evolutionary origins and were once helpful—essential to survival, even—but when applied to modern situations can lead us astray. I tell the story of an experienced backcountry skier who was killed in an avalanche. He was swayed by the "familiarity" heuristic, which basically says that humans trust what is familiar. During ancient times this instinct was a survival mechanism. It helped us find recognizable plants that were suitable to eat, for instance. But for the seasoned backcountry skier who had traversed the same route hundreds of times, it was a trap. It led him to ignore the warning signs that consequently caused his death.

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What's an example of a heuristic that can spell trouble if we're not careful?

One I call the "caricature heuristic," or, in common terms, stereotyping. We need to categorize the world because it's very complex, so early on the brain developed a mechanism for putting things in pigeonholes. We couldn't get through life without this mental shortcut. For example, it's useful for doctors to categorize patients with sickle cell anemia as black, or patients with dementia as old. You run into problems when you use caricatures in the wrong way, as with negative stereotyping. I discuss a longitudinal study that found that young people who characterized the elderly as feeble and senile were more likely to suffer from coronary heart disease, stroke, and heart attack themselves later on. We actually grow into the stereotypes we held at a young age. We take them to heart—and it kills us.

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Can these instincts be beneficial?

That's the point of the whole book. Cognitive psychologists would use the word "de-bias"—if we're aware of these powerful mental proclivities and how they work, we can say no to them. We can utilize self-talk and say: "I don't have to subject myself to that. I can take a different route." I personally use the "scarcity" heuristic to my advantage each day when I go to the gym. It simply says that if something is rare, it's perceived as more valuable. So on mornings I feel like skipping my workout, I remind myself that the rest of the day I'll be sitting behind a desk. I say to myself, "This is your only time to move around. It's rare. It's like gold."

So awareness is power?

Exactly. There's currently a battle going on in academia about heuristics. One camp says that our gut instincts are more trustworthy than taking the time to deliberate. The other camp says heuristics are traps that lead us toward all sorts of mistakes. I tend to take the middle road: Heuristics are neither good nor bad: it depends on the situation. There are times we ought to unthinkingly settle for that "good enough" solution. But there are others where we need to slow down and tell ourselves, "On second thought,…"