Can you trust your own judgment about health/fitness?


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Just wanted to highlight a book excerpt that ran in the New York Times Magazine over the weekend, from Nobel Prize-winning psychologist Daniel Kahneman’s forthcoming book “Thinking, Fast and Slow.” It’s about our general tendency to place great faith in our own explanations for things, regardless of whether the facts bear them out:

The confidence we experience as we make a judgment is not a reasoned evaluation of the probability that it is right. Confidence is a feeling, one determined mostly by the coherence of the story and by the ease with which it comes to mind, even when the evidence for the story is sparse and unreliable. The bias toward coherence favors overconfidence. An individual who expresses high confidence probably has a good story, which may or may not be true.

[…] When a compelling impression of a particular event clashes with general knowledge, the impression commonly prevails.

The main example he discusses in the excerpt is the world of finance — many, many people (including just about everyone I know, seemingly) are convinced that they or their financial advisors are capable of outperforming the market, despite ample evidence that this is nearly impossible to do on a consistent basis. But the good stock picks they’ve made over the years make such a vivid impression that they remain convinced of their abilities.

The reason I’m blogging about this here is that I think this phenomenon is also nearly universal when it comes to health and fitness. Of course, there are many people who either don’t believe in or don’t understand the scientific method. They trust their instincts in figuring out which potions and pills are helping them in vague and unquantifiable ways. This is not surprising at all. What is surprising to me is the number of people who understand and profess belief in the scientific method, who murmur all the right catchphrases about “correlation is not causation” and “of course n=1 anecdotes don’t mean anything,” and yet are still absolutely convinced of their ability to determine which stretch has enhanced their power or saved them from injury, or which pill makes them feel more energetic, or which type of training has enhanced their lactate clearance.

There is some good news at the end of Kahneman’s excerpt: it is possible to have real intuitive expertise. (“You are probably an expert in guessing your spouse‚Äôs mood from one word on the telephone,” he notes. Chess players and medical diagnosticians are other example.) But there’s a necessary condition:

Is the environment in which the judgment is made sufficiently regular to enable predictions from the available evidence? The answer is yes for diagnosticians, no for stock pickers.

Maybe I’m just a particularly complicated human, or unusually incapable of reading my body’s signals. But given the huge number of factors, both intrinsic and extrinsic, that affect the day-to-day variation in my mood, energy and physical performance, I don’t consider my own body “sufficiently regular” to be able to make accurate judgements about the efficacy of any particular single intervention.

3 Replies to “Can you trust your own judgment about health/fitness?”

  1. The factors ARE too numerous, complex, and often hidden. But the body has a built-in monitor through which it tells us about its state. OK, you blockheaded rationalists can tune out right now, ’cause I’m talking about calm, inner feeling. Notice I didn’t say “wild adolescent emotion.” There’s a difference – emotions nearly always lead us astray. But there’s a different level of feeling that talks truth. It took me a long time to take those feelings seriously, because they so often told me things I didn’t want to hear: “Go slowly. Go home. Jog.” But I discovered something wonderful. As often as I listened for those intuitions and did what they said, I had wonderful runs very reliably and made progress in fitness. The body has a strange economy of joy: do the “right thing” even if it means that you feel crappy and must jog 30 minutes instead of running long – and the body rewards you with joy. This is expansive training – training that produces results as improved fitness and increased enjoyment. The rational mind, on the other hand, too often allows itself to be led by emotion – it…well, it rationalizes, finding reasons to do what our teenage hearts want. I’ll be 70 in 3 months, and by following this system I’m enjoying exercise more than ever (I’ve run since 1968).

  2. @runbei: I’m a pretty hard-headed rationalist, but I’m still willing to acknowledge the power of allowing yourself to be led by emotion! In fact, Jonah Lehrer had an absolutely fascinating blog entry last month about how relying on emotion rather than “rationality” can produce superior decision-making in some contexts:

    I actually considered making this blog entry a “point-counterpoint” between Kahneman’s essay and Lehrer’s blog entry, but I didn’t want to ramble on too much!

  3. A friend recently sent me a copy of the book, The Invisible Gorilla, which covers ground related to the above. On their website, the authors give this description:
    “Reading this book will make you less sure of yourself-and that’s a good thing. In The Invisible Gorilla, we use a wide assortment of stories and counterintuitive scientific findings to reveal an important truth: Our minds don’t work the way we think they do. We think we see ourselves and the world as they really are, but we’re actually missing a whole lot.

    We combine the work of other researchers with our own findings on attention, perception, memory, and reasoning to reveal how faulty intuitions often get us into trouble.”

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