“Also,” he said, “please do it using all available exits.”

Bomb scare. That was Berkeley in the ’70s: lots of scare, not many bombs.

And that was the last I saw of Joan Didion for many years, standing beside my father in the bright sunshine of the south portico of Wheeler Hall, the two of them doling out, respectively, diplomas and handshakes. All of these events—the dinner party and the fan stories and the commencement address with the bomb scare—would have faded in my memory, just Berkeley stories (there was always something happening in Berkeley, always something you didn’t want to miss) and nothing to dwell on, except for something that took place a few weeks after she left town that made me think back on all the things that had happened, all the details, and see them for what they really were: a youthful encounter with greatness.

I was sitting in the living room of some friends of my parents, during our annual summer in Dublin, and I noticed on the coffee table a book with a bright orange-and-yellow cover. I craned my neck around to read the title: Slouching Towards Bethlehem, by Joan Didion. I asked if I could borrow it. I began reading it right there on the couch, and took it away with me, and never gave it back. It changed my life.

Slouching Towards Bethlehem is composed of 20 essays written between 1961 and 1967, some of them extremely brief and all of them written against deadline and for money. Although the book is often characterized—because of its title essay and arresting preface on the subject—as being about the social upheavals of the ’60s, the collection is surpassingly eclectic. It includes an essay on a famous murder, a movie-star profile, several travel pieces, a meditation on the wedding industry, and a description of the emotional complexities that attend a grown woman’s visit to her parents’ home. In another writer’s hands, it would have been a dog’s breakfast of occasional pieces, and its lack of focus is in part attributable to the fact that collecting some of her journalism in a book was not Didion’s idea at all: she was, in her deepest sense of herself, a novelist. The essays were a means to that end.

Like many people in a wide variety of callings, she did not realize that it was the thing she did repeatedly, and always at the cost of what seemed to her the more important and more exalted work, that would come to define her. Someone suggested a collection, Didion tossed off the preface in a night, and that was that. Although she had a growing reputation as a fiction writer, she had not developed a steadily growing number of readers of her nonfiction, because she tended to publish in places that did not have a significant overlap of subscribers: the average reader of Vogue—a home for her work because she had been in the magazine’s employ for her first seven years out of college—was not also a reader of The Saturday Evening Post, where she liked to publish because, as she explained in the book’s preface, The Post “is extremely receptive to what the writer wants to do, pays enough for him to be able to do it right, and is meticulous about not changing copy.” The New York Times Book Review hailed Slouching Towards Bethlehem as “a rich display of some of the best prose written today in this country,” and the book was everywhere well received, but it was no rocket ship in the beginning, finding its audience in gradually enlarging waves, woman by woman, and slowly building to a phenomenon not often seen in the book business: becoming something far too widely read to be called a cult book, but engendering a cult’s kind of fierce and jealously protective loyalty. Encountering someone who loves it as much as you do is a bedeviling experience: you have met both a landsman and a rival; each of us believes that our relationship with the book is unique.