Why do so many people—2 million a year, in nearly all Fortune 500 companies and U.S. colleges and universities, in community centers and churches and couples’ retreats, in the Army, the Navy, and the CIA—continue not only to embrace the type indicator, but to defend its inviolability with the kind of ardor usually reserve for matters of the deepest faith.

“Myers-Briggs is like my religion” is a familiar refrain one hears at MBTI sessions. “It helped me find myself.” “It changed my life.” “I was never the same again.”

What causes people to have the unwavering belief in the MBTI’s ability to comprehend who we are—why we work the jobs we work, why we love the people we love, why we behave in the apparently various and contradictory ways we do.

At the heart of this mystery is a set of questions fundamental to all human existence.

What is a personality?

Where does it come from?

Why are we so intent on categorizing it?

And, of course, the greatest question of all:

Who am I?