In 1948, Bertram Forer was teaching a class on introductory psychology in the department of medicine and surgery at Los Angeles’s Veterans Administration. A former Army psychologist, Forer was intrigued by the personality assessments and the psychological tests that he’d seen administered—and had administered himself—in military and civilian settings alike: did they have any real bearing on a person’s inner self? His students, he decided, would be the perfect subjects. They were, after all, getting educated in psychological techniques and the importance of proper methodology; if anyone was to be skeptical of the power of personality assessments, it would be them. During one lecture, he casually mentioned the Diagnostic Interest Blank, an instrument which, he claimed, was widely used in clinical settings. The D.I.B. asked its subjects to list their hobbies, preferred reading materials, personal characteristics, and job duties, and the secret hopes and ambitions of their ideal person. Based on that list, a psychologist would offer a qualitative interpretation of their personality dynamics. Intrigued, his students asked if Forer would administer the test to them—and, of course, provide personalized evaluations based on the results.

When the class next convened, Forer presented thirty-nine blank versions of the D.I.B. Based on the students’ responses, he promised, he would return a brief, personalized personality-revealing vignette. One week later, he had completed his assessments: each student was handed a neatly typed piece of paper, her name written across the top. On the paper was a list of thirteen statements about her personality. Forer asked the students to read their profiles, turn them over, and answer two questions: on a scale of zero (poor) to five (perfect), how effective was the D.I.B. at revealing personality, and to what extent did it reveal basic characteristics of their own personalities? He then had the students mark each of the thirteen statements as either true or false, as it applied to them, or to leave a question mark if they weren’t sure. Next, he collected the papers and asked each student to raise her hand if she thought that the personality assessment had been accurate. Almost every hand went up.

Then Forer revealed the truth: not only had everyone received an identical profile but that profile had nothing whatsoever to do with the D.I.B., a test that he had personally created for the occasion. The questions had been culled from a newsstand astrology book. The students had been taken in by nothing more than vague statements from a horoscope.

When Forer examined the rankings, he found that, on average, the students had rated both the D.I.B. as a whole and their own personality sketch as achieving a 4.3 out of five. Only one person had ranked the over-all test lower than four, and only five had rated their own profiles below four. They accepted an average of ten of the thirteen items as personally true. Forer called what he was seeing subjective validation.

The phenomenon—now known as either the Forer effect or the Barnum effect, the latter to commemorate P. T. Barnum’s pledge always to offer something for everyone—has proved itself to be one of the most reliable and replicable in psychology: present the right sort of feedback, and it will be believed. Since Forer’s initial work, several general principles of effective Barnuming, so to speak, have been established. According to a University of Saskatchewan review of more than sixty studies of subjective validation, profiles that elicit the strongest confirmation response are relatively vague (“You enjoy a certain amount of change and variety in life”), double-sided (“You are generally cheerful and optimistic but get depressed at times”), and favorable over all (“You are forceful and well liked by others”). Some negative commentary is fine—as long as the broad message is reassuring. (“You have a great need for other people to like and admire you,” reads the first statement in Forer’s 1948 profile.) The more positive the general assessment, the more likely we are to believe it. Even astrology skeptics begin to rethink their beliefs if their horoscopes are positive.

The most successful of these tests follow a few standard formats (forced choice, or forcing you to answer a question one way or the other; checklists; multiple choice) and are not overly long. The shorter the instrument, the University of Saskatchewan team found, the more efficient and accurate we think it is.

Given these qualities, it’s no surprise that the Forer effect has found a new home: the predictive Internet quiz. Would you survive the Hunger Games? Where in the world should you really be living? Not only are these new versions of the personality quiz everywhere—particularly in our Facebook feeds—but they are tempting. BuzzFeed’s “Which ‘Game of Thrones’ Character Are You?” quiz has drawn more than two million page views. Why do we love them so?

For starters, we love to hear about ourselves, and we love compliments. Early versions of the online quiz—think back to “Which ‘Sex and the City’ Character Are You?”—have stuck around for the same reason that astrology has stuck around. It’s also why psychics rely on practices that seem immune to recession and the threat of prosecution alike. As the youth and digital-media scholar Katie Davis told me, “I remember taking these personality quizzes in Seventeen.” No matter our age, we tend to be our own favorite subject, which is why it was so easy for Forer to get his students to take part in his experiment. He didn’t even have to tell them that he was doing a study or ask them to take a personality assessment. They asked him themselves.

That me-centric view predates both the Internet and the practice of psychology. Ptolemy, after all, wrote his treatise on astrology, “Tetrabiblos,” back in the second century. In its pages, he expounded on the earthly effects that the twelve celestial signs have on our lives and fates—an exposition that wouldn’t be at all out of place in a modern psychic’s repertoire or the pages of your weekly horoscope. What, then, is it about the present moment that makes it so ripe for inner-depth-revealing online assessments? Why does 2014 seem to be shaping up as the year of the quiz?

The answer may go back to another age-old human desire: the need to belong. When Abraham Maslow first posited his famous hierarchy of needs, in 1943, he placed belonging close to the foundation of his pyramid, just above physiological survival and physical safety. And while belonging has motivated us for years, in the age of the Internet, the nature of the goal has subtly shifted—and, in the past year, the shift has become ever more pronounced.

In 2012, when she was working with the psychologist Howard Gardner at Harvard’s Project Zero (she has since moved to the University of Washington), Davis decided to study how the newest online users—the adolescents who are growing up with social media, whom she and Gardner dubbed the “App Generation”—were developing their identity online. It turned out that they weren’t doing it much differently from the rest of us, but they were doing it much more publicly, from a much younger age. “Identity development has always been a very social process,” Davis said. “With the Internet, that process has become much more public. There’s a focus on a more performative public identity that has an emphasis on personal branding and cultivating a public persona.” Her subjects, she noticed, would tag friends in posts and in photographs as a signalling mechanism, as a way to say, “Look, I’d survive the Hunger Games. Would you?” Their shares and tags were a way to create in-groups and “to define the boundaries of [a] friendship group.”