Journalist Katie Hafner has recently written her first novel, “The Boys,” and the switch from fact to fiction gave her the freedom to just “make stuff up.”

When I was in college in the 1970s, I majored in German literature, focusing almost exclusively on Franz Kafka. I was so taken with the fabulist leaps of Kafka’s shorter pieces that I spent a semester working on a paper in which I analyzed his diaries. His entries, I discovered, fell into three categories: pure observation, observation transformed into invention, and pure invention.

I was most intrigued by the entries in the second category. These always began with an observation of some kind – a woman on the tram, say, or the expression on a friend’s face – then quickly turned to fabrication. One example: On Oct. 30, 1911, Kafka writes about his famously delicate intestinal tract, noting that “for once I feel my stomach is healthy.”

In the next sentence Kafka slides into invention. He imagines himself at the butcher shop, shoving “long slabs of rib meat unbitten into my mouth,” eating “dirty delicatessen stores completely empty” and having “bonbons . . . poured into me like hail from their tin boxes.” Not only was I captivated by how suddenly he immersed himself in his made-up experience, but I was also quietly thrilled by the idea that I was trespassing upon Kafka’s inner life.

I became a journalist, and for four decades I tethered myself to Kafka’s first category: pure observation. That intriguing second category was strictly off limits. There could be no flights into the “what if” of a story.

Then, five years ago, my daughter and I were taking a bike trip, and one evening at dinner one of the guides described a previous guest who had been particularly problematic. Our guide told the story in only two or three sentences, but it was so wildly evocative that my daughter turned to me and said what I was thinking: “That’s a novel.”

I spent the next three years, on and off, spinning a book-length tale from that threadbare anecdote. “The Boys,” my first novel, after six books of nonfiction and hundreds of articles for the New York Times, is the product of the license I granted to myself – to make stuff up.

Even now, having sent my novel out into the world, I find that a reporter’s fact-abiding mind-set can be hard to shake. A friend came to dinner recently. She had just read the novel and was eager to discuss the plot, the characters, their motivations, their psychological makeup. I began to feel uneasy, accountable for her investment in people who didn’t exist. I had a sudden urge to apologize to her, to confess that I had, like Janet Cooke and Jayson Blair and other reporters who violated the public’s trust with their fabricated stories, invented those people and everything about them.

For a journalist to turn to fiction is liberating, to be sure, and many have made the transition seamlessly. Anna Quindlen is one good example. Geraldine Brooks is another. But writing fiction can also be paralyzing for a reporter. We’re tyrannized by what’s true but also protected by it. The closed fist of facts is a haven of sorts. When granted the freedom of fiction, and with it what feels like an infinite number of directions a story can go, a journalist can lose control and run off the rails, into language that’s too flowery, plot twists that are preposterous, a cast of hundreds devoid of nuance.

I found myself particularly susceptible to the temptation to go overboard. The topics I’ve covered as a journalist have been mostly lacking in intrinsic suspense. I haven’t written any true crime to speak of, nor chronicled a courtroom drama. It isn’t easy to bring narrative tension to a story about, say, the origins of the Internet or the risk of falls among the elderly. But that’s the part of the challenge I’ve enjoyed most: How do I make something interesting out of the story of one famous pianist’s beloved instrument, or 150 years in the life of one house in Germany, all while constrained by the facts? Or how to make these topics interesting enough to compel people to want to know what happens next?

Yet, paradoxically perhaps, the decades I’ve spent as a journalist have made me more restrained as a fiction writer, not less. That is, I find more similarities than differences between writing fiction and nonfiction. In both, one’s choice of language, imagery and metaphors is as important as pace and storyline. The one key difference is that journey into the “what if?”

Time and again while writing “The Boys,” I was put in mind of Kafka’s second category – the shift from observation to invention. My visit, during my husband’s college reunion in Philadelphia, to a museum of medical oddities became the unusual venue for a wedding. A single derailleur cable found snapped in two during a bike ride I took in Italy morphed into something more sinister. My terrifying experience in the early weeks of the pandemic of seeing a man coughing as he leaned over to examine the bok choy at the grocery store turned into a scene that advances the story of my protagonist.

And how did I keep myself from wandering onto the ill-advised terrain of linguistic Febreze, cartoon villains and outrageous plots? Much as when I’m researching a nonfiction story, I did the bulk of the reporting first, then sat down to write. I researched the psychological condition known as the anniversary reaction, in which an anniversary triggers feelings rooted in childhood trauma. I went to a diner with tabletop jukeboxes; I scouted out a house in Philadelphia I thought would be perfect for my main characters, then asked the owners, whom I had never met, for a tour. I roamed the exhibit hall at the Mütter Museum, the museum of medical oddities. I know this kind of basic research is something novelists do all the time, but it seemed especially important with this, my first stab at fiction.

One of the most valuable lessons I’ve learned from my years of writing nonfiction is to choose wisely, to include only those details and quotes that propel a story forward or illuminate a larger point. Back when movies came on DVD, I studied the discussions of deleted scenes, seeking insights into how a director decides what to cut. Darlings get killed left and right when movies are made, not because the scenes aren’t good, but because their service to the story is weak or has been achieved elsewhere.

When writing nonfiction – whether 1,500 words or 50,000 – I constantly struggle with that question: How does each and every detail or quote serve the story? With fiction, the task is twice as demanding: Not only must your words serve the narrative, but you must always be mindful of your characters and their place in the story. It seems obvious, but when sprung free, journalists are in danger of losing sight of that simple rule.

After that brief moment of panic during dinner with my friend, I relaxed into the recognition that my characters had become as real to me during the course of writing the book as they now were to her. And in a way, they were more real to me than anyone I had written about as a journalist. There’s only so much I can know about people who actually exist. When it comes to those of my own invention, I am omniscient. It’s an intoxicating feeling, one that surely inspires many a novelist to go back for more.

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Katie Hafner is a journalist and author. She is host and co-executive producer of the podcast “Lost Women of Science.” Her first novel, “The Boys,” was published last month.