One of my favorite demonstrations is to take a string of such generally true statements drawn from horoscope books and offer them to my students as “personalized feedback” following a little personality test:

You have a strong need for other people to like and admire you. You have a tendency to be critical of yourself. You pride yourself on being an independent thinker and do not accept other opinions without satisfactory proof. You have found it unwise to be too frank in revealing yourself to others. At times you are extraverted, affable, sociable; at other times you are introverted, wary, and reserved. Some of your aspirations tend to be pretty unrealistic.

Nearly all my students state such stock comments as “good” or “excellent”—a phenomenon called the “Barnum effect” in honor of P. T. Barnum’s dictum “There’s a sucker born every minute.” Some students even express amazement at the astonishing insights gleaned by my remarkable (pseudo) test. “It’s astonishing how well that test pegged me.”

French psychologist Michel Gaugelin had fun with the Barnum effect. He placed an ad in a Paris newspaper offering a free personal horoscope. Ninety-four percent of those receiving the horoscope later praised the description as accurate. Actually, every single one had received the horoscope of Dr. Petiot, France’s notorious mass murderer.

David Myers, The Pursuit of Happiness, New York, 1992, pp. 93-94