In 1943, a failed mystery novelist named Isabel Briggs Myers started a career in the new field of personality testing. “The more you know about what a man is like, the more effectively you can work with him or under him, or assign him the right job,” Myers wrote to Edward Hay, a Philadelphia-based HR specialist who administered employee aptitude testing for companies. Hay offered finger dexterity tests for entry-level clerks and questionnaires about union attitudes for potential supervisors. Myers had something far more radical in mind, a schema to unearth a person’s true character called the Myers-Briggs Type Indicator, which offers a questionnaire that divides test-takers into 16 different possible personality types based on the results. There were no bad personality types, only bad combinations of personality type and employment. “If men came like shoes,” she wrote, “with the most vital data as to size and style marked outside the box, many a cramping fit could be avoided.” In Myers’s vision of a capitalist utopia, everyone would whistle while they worked.

The Myers-Briggs Type Indicator is simple, a 93-question forced-choice test, loosely based on personality types outlined by Swiss psychoanalyst Carl Jung in his 1921 book Psychological Types. The MBTI splits people into four dichotomies: introverted (I) or extroverted (E); intuitive (N) or sensory (S); thinking (T) or feeling (F); judging (J) or perceiving (P). An ENTJ is meant to be a sociable, rational high achiever, while an ISFP is supposed to be supportive and practical. According to Myers, these types were the key to revolutionizing industry. By pairing employees with the right tasks and employers, she would create a more harmonious world.

Hay liked what he heard. Soon, so would many others. During the 1940s, the Myers-Briggs test was used by Station S, the nation’s first personality assessment center for spies, as a way to figure out who could handle the pressure of international wartime espionage. The Educational Testing Service, a well-respected New Jersey–based standardized testing company, published the first MBTI manual in 1962, and all across the country corporate honchos beckoned. “The pervasive belief that liking or even loving one’s job could function as a powerful liberating force had a history that was intimately tied to how the Myers-Briggs Type Indicator and its ilk ensnared the American workplace after Isabel debuted it to Hay during World War II,” writes Merve Emre, whose new book, The Personality Brokers, which comes out in the United States in September, traces the history of Myers-Briggs. “According to sociologist William H. Whyte’s 1956 bestseller, The Organization Man, 60 percent of American corporations were using personality tests in 1956, not only to screen potential employees but also to ‘check up on people’ already employed by the company.”

Today, Myers’s story still gets bought around the world. The test is taken by more than 2 million people a year, including recruits to Fortune 500 companies, the Army, and the CIA. Results are submitted as evidence in custody battles and criminal sentencing hearings. “Type is a $500 million technology of the self that spans twenty-six countries and more than two dozen languages, from Afrikaans to Cantonese,” Emre writes. Knockoff tests abound on the internet, promising results for free. (The “real” test, administered by its official publisher, CPP Inc., costs around $50.) There are Myers-Briggs dating services, Myers-Briggs diet tips, Myers-Briggs couples therapy, and even a personality assessment called Dognition that’s praised as “Myers-Briggs for your dog.”

Myers-Briggs offers a model for self-revelation that has endured for decades, thrilling boomers and delighting millennials even as it has perpetually disgusted frustrated psychologists. It helped spawn a booming industry of personality assessments, one that uses the internet and algorithms to hopscotch far beyond the original, hand-scored tests. It inspires an ardent fandom that borders on spiritual, and yet its primary use is decidedly tethered to the material world, as a way to shuffle workers into places where they won’t complain. Its paradoxical appeal, as a woo-woo tool to know the soul and as a convenient, prefab employee sorter for corporations, is both absurd and a little poetic. After all, Myers-Briggs insists that the world looks very different depending on where you fit in its divided blueprint. It’s appropriate, then, that the test can mean so many different things to so many different people.

The other half of the Myers-Briggs, Katharine Cook Briggs, was Isabel’s mother, who had introduced her daughter to the idea of psychological types. Briggs first started her research into the world of personality types after noticing that her daughter Isabel’s fiancé had a markedly different personality from the rest of her family. She merged her quest to figure out why Isabel’s beau was so hard for her to understand with her burgeoning fixation on the work of Jung, whom she idolized. Katharine devised the early MBTI questionnaire for family and friends, drawing on Jung’s work. (Jung was never actually involved with the test and did not seem to find it particularly interesting, although Katharine did write him repeatedly about it, as Emre details in The Personality Brokers.) It was, in its original essence, the work of a salty and extremely committed mother-in-law who needed to understand what the hell was going on with her daughter’s romantic choices. As her mother grew older, however, Isabel took up the mission, with an alteration in mind. Instead of focusing on the test’s capacity to help people reflect on themselves, she saw it as a tool for the rapidly changing world of industry.

Isabel traipsed around the country convincing gatekeepers of the most prestigious institutions to believe in her vision of anatomizing humanity. All the while, she refused to compromise on how her test worked, wore dresses with tennis shoes, and regularly chugged a homemade concoction of brewer’s yeast, milk, and melted Hershey chocolate bars she called “tiger’s milk.” She did not believe in feminism. She believed fervently in capitalism. Many colleagues despised her, calling her that “horrible woman.” If anyone deserves the label of a true iconoclast, Briggs does, something that Emre recognizes. “At many points in writing this book, I wanted it to be a feminist triumph,” Emre writes in The Personality Brokers’ introduction, noting that both Katharine’s and Isabel’s personal histories as intelligent homemakers striving to self-actualize by bringing their project to the world were both sympathetic and compelling. And yet, their life’s work aimed to distill personalities into a simple formula. The mission of these oddball trailblazers was a peace achieved by slotting others onto well-established and immutable tracks.

Myers-Briggs was, in its original essence, the work of a salty and extremely committed mother-in-law who needed to understand what the hell was going on with her daughter’s romantic choices.

Emre’s book revels in the peculiar dispositions of the creators of Myers-Briggs as a way of undermining and complicating their project. The Personality Brokers is a unique meld of a hidden history of two admirably prickly women and an examination of why their ideas were simultaneously damaging and popular. While Emre excavated archival documents to piece together the story of Myers and Briggs, she also ventured into the modern world of their devotees. Emre attended MBTI training sessions, and she recounts how happy Myers-Briggs made some of her fellow attendees. “I witnessed flashes of epiphany that were not, in any sense, untrue; I saw things fall into place for people,” Emre writes. One attendee told her after the seminar that it had “given her the confidence to start looking for new jobs.”

However, as Emre and many, many Myers-Briggs debunkers have noted, psychologists tend to dismiss the MBTI as nonsense, stressing that the test is unreliable and useless. While acolytes insist that your type will never change, people often get different results each time they take the test — suggesting, well, otherwise. Plus, the test insists on binaries of behavior that do not exist; for example, extraversion and introversion are often viewed on a continuum, which allows for the possibility of ambiversion. Even Myers-Briggs’s own data suggests that most people fall somewhere in between introversion and extroversion. “It has the intellectual content of a fortune cookie,” former University of Tulsa psychology professor Robert Hogan told The Boston Globe in 2004. (Even Jung did not believe that it was possible to classify people in this way. “Every individual is an exception to the rule,” he wrote.) If the MBTI were primarily used as a tool for self-knowledge, this would be disappointing but not dangerous. However, its prominence as a tool for corporate America has made it more sinister than silly.

“Under the rule of type, the labeling of live human beings emerged as one technique for annihilating individuality — for treating people as interchangeable, and sometimes disposable, parts of an unforgiving social whole.” —Merve Emre, The Personality Brokers

Companies wield the results of MBTI tests to determine the fate of their workers, and to inoculate themselves from criticism. “The administration of personality tests is frequently presented as a gesture of corporate goodwill, a generous acknowledgement of employees’ uniqueness. Under this banner of respect for individuality, organizations are able to shift responsibility for employee satisfaction onto that obliging culprit, ‘fit,’” Annie Murphy Paul wrote in The Cult of Personality Testing, a 2004 book that explores the rise of various personality testing schemas, including Myers-Briggs. As Murphy Paul notes, the test’s genius is that it compels people to label themselves, doing the work of slotting themselves into categories in ways that will help employers justify their treatment while abdicating responsibility for it.

While Myers-Briggs lacked the flagrantly racist stink of phrenology and appeared, on the surface, to be more rigorous than Rorschach’s inkblot interpretations, its very innocuousness helped spur its longevity and obscure how troublesome its continued prominence in sorting humans is. “Under the rule of type, the labeling of live human beings emerged as one technique for annihilating individuality — for treating people as interchangeable, and sometimes disposable, parts of an unforgiving social whole,” Emre writes. “Type was, in short, one of the bluntest and best-disguised tools of modernity: a wolf in sheep’s clothes.”

Myers-Briggs resembles earlier stabs at personality divination, like the Woodworth Psychoneurotic Inventory, which was used to evaluate potential soldiers during World War I, and is often cited as the first widely used personality test. However, while the Woodworth was later reformulated for civilians, Myers-Briggs started off as a test for “normal” civilians, and was thus tailored toward “ordinary” people from the start. The sheep’s clothing was bespoke.

Enthusiasts of personality testing hail its potency as a tool for exploring and understanding identity, a way to connect the often jumbled dots of personal behavior and preference into a comprehensible pattern. For its proponents, Myers-Briggs acts like a map that provides direction toward people’s proper places in the world. It’s a diagnosis of how a person is meant to be. The appeal of the personality test is the appeal of coherence, the comfort of feeling like you understand yourself. In this way, it shares an allure with other popular people-sorting constructions, like horoscopes, or the Harry Potter sorting hat — a way to assign oneself a community and a reference point. “I tend to think that this inward-glancing search for alternative forms of wisdom and knowledge is just a survival tool in a world that, for a lot of young people today, comes without a reliable map of the future,” my colleague Lindsay Zoladz wrote earlier this year, in a piece about astrology’s current vogue among millennials. Reading Emre’s account of her fellow MBTI attendees’ enthusiasm for the indicator as a tool, I was reminded of Lindsay’s words. The world is scary and hard to understand. With its pseudoscientific vocabulary, approval from prestigious institutions, and positive framing — there are no bad personality types! — Myers-Briggs provides an architecture for understanding people that seems legitimate, unthreatening, and easy-to-use.

Although it remains popular in its original form, Myers-Briggs inspired a bevy of imitators and homage payers, with a variety of individuals and groups building on its basic premise to present their own products. The Keirsey Temperament Sorter, for example, developed by psychologist David Keirsey for his 1978 book Please Understand Me, cherry-picks elements of Myers-Briggs, like the 16 possible personality types, to create its own taxonomy. Additionally, businessman Don Lowry created his own spin on Myers-Briggs, a schema called “True Colors” (in which types were sorted into colors) in 1978 as well, after he read Please Understand Me.

The appeal of the personality test is the appeal of coherence. In this way, it shares an allure with other popular people-sorting constructions, like horoscopes, or the Harry Potter sorting hat — a way to assign oneself a community and a reference point.

Myers-Briggs’s rise in popularity also dovetailed with a general cultural enthusiasm for personality quizzes, which started appearing regularly in women’s magazines during the 1950s. The timing was fitting; the postwar decade, in which popular personality assessments first thrived, nurtured a national fixation on normalcy and white-picket-fence conformity. The appeal endured, however, through cultural tumult and technological revolutions. “Offering up glib ways to create identity — shortcuts to the self — is a winning business proposition,” journalist Sarah Laskow noted in a 2014 Columbia Journalism Review story on the history of magazine quizzes. Today, you can take a personality quiz online about just about anything. BuzzFeed even has personality quizzes about Myers-Briggs.

A new industry has developed in the world of personality testing. While the field has long attracted grifters and weirdos, this most recent iteration wears its nakedly manipulative heart on its data-stuffed sleeve. This industry gained infamy earlier this year, when The New York Times revealed that the political consulting firm Cambridge Analytica, most famously used by the Trump presidential campaign in 2016, surreptitiously collected data from Facebook personality quizzes. “At the heart of the public scandal over the political uses of your data is the humble personality test — a central technique used by corporations to harvest value from our personal data,” historian Kira Lussier wrote for Slate. “We cannot truly understand the implications of this scandal, nor can we formulate a social response to it, without understanding the broader context of personality testing, particularly the role private companies have played in making us so comfortable answering questions about ourselves.” Cambridge Analytica created psychological profiles for millions of people based on their Facebook data, and then targeted advertisements for clients based on what would appeal to specific personalities. “I made Steve Bannon’s psychological warfare mindfuck tool,” Cambridge Analytica whistleblower Christopher Wylie told The Guardian. It sounds more nefarious than it is, but only because there’s actually not much compelling evidence that it can make these predictions correctly.

Just because psychometrics doesn’t work very well yet, though, is no reason not to take its menace seriously. When Isabel Myers first started selling individual copies of the MBTI, she scored the results by hand. Now, online test-takers get a summary of their outline spat into their inbox after a few clicks. While Myers-Briggs fans continue to champion the test as a valuable self-exploratory tool, it is necessary to remember that the MBTI was meant as a helpmate for the powerful from its beginning. It didn’t get co-opted by corporations, it was concocted for them, selling what Emre calls the “fantasy of rational organization of labor.” While “know thyself” is still an alluring directive, when it comes to personality testing, it is increasingly important to scrutinize who else might be trying to know the answer.