The most common mistake that people make in this regard is believing other people. For instance, a testimonial— whether it comes to you from a friend or blares out at you from a TV screen—is a poor criterion for determining truth.

A case in point is the experience of a writer for a popular fitness magazine who once wrote a facetious article about a “miracle supplement.” At the bottom of the page on which the article appeared, he had the magazine’s art department create a perforated square roughly the size of a postage stamp, next to which appeared the following recommendation: “For optimal muscle gains, cut out this little piece of paper and place it in a glass of water overnight. It contains a special mix of amino acids that are released in water over several hours. In the morning, remove the paper and place it on your tongue to allow the amino acids to enter your body.” He intended it as a joke, a last-minute bit of whimsy to fill a page where an advertisement had been withdrawn. His intention, however, was not communicated very well to the readers, as, within days of the magazine’s hitting the stands, the publisher was inundated with requests for “more of that awesome paper.” Many readers honestly believed that placing it on their tongues as instructed made their muscles bigger and stronger. This response is characteristic of the placebo effect, a demonstration of the power of suggestion, which impels people to buy all manner of things. If one of your friends or relatives happened to number among those who believed in this “miracle supplement,” he or she likely would have told you how “great” this product was, and you— if you put stock in testimonials—would probably have tried it.

-- Doug McDuff, M.D., and John Little, Body by Science, pp. ix-x