Humanity’s strange, ardent love affair with Story has always fascinated me. To explore our enthrallment and explain the science behind it, I wrote a book – The Storytelling Animal: How Stories Make Us Human. The book appealed to a predictable audience of English literature types as well as avid readers of popular science. But it also attracted an unanticipated audience of business professionals. As a professor of literature, I hadn’t known that a wide spectrum of professions was embracing storytelling as a uniquely powerful form of messaging, that they had discovered that far from being a soft, touchy-feely skill, storytelling was a powerful form of witchery. A great storyteller waves her pen over paper like a wand. She casts a spell that allows her to enter minds and change what they feel, which allows her to change what they think, which allows her to influence how they act. Companies were flocking to story because they wanted a piece of this power.

As the business world has hurried to get up to speed on storytelling, its advantages over other forms of communication and persuasion have been widely touted. But like any powerful tool, humans can wield stories for good or ill. It’s time to grapple with the dark side of story.

Consider the medical technology company Theranos, founded by Elizabeth Holmes, which seems to be reaching the end of an epic flameout. Following a long stretch of fawning coverage from business and technology journalists, The Wall Street Journal reported in October 2015 that the company’s flagship blood-testing technology was a near-total failure. This month, investors accused Theranos of running a long con. In attempting to recoup a $96 million investment, Partner Management Fund LP accused Theranos of “a series of lies, material misstatements, and omissions,” and filed suit for securities fraud.

According to Nick Bilton’s absorbing exposé in Vanity Fair, Theranos—a company once valued at $9 billion—got as far as it did mainly on the strength of “a preternaturally good story.” Holmes constructed an inspiring hero narrative starring herself—a precocious girl-genius who, at nineteen years of age, began pioneering medical technologies that could potentially save millions of lives around the world. Despite abundant warning signs, and despite the Silicon Valley company’s refusal to provide real evidence that their technology worked, journalists didn’t skeptically evaluate Holmes’s story—they simply repeated it. They told and re-told Holmes’s story until she began to seem less like an actual person, and more like a living symbol—of progress, of innovation, of female empowerment. The problem, as The Wall Street Journal’s John Carreyrou has reported in more than a score of articles, was that there was little to Theranos beyond its story—and that story was mainly fictional.

According to the great English poet and philosopher Samuel Taylor Coleridge (1772-1834), enjoyment of fiction requires a “willing suspension of disbelief”—a conscious decision. We say to ourselves, “Well, I know this story about Beowulf battling Grendel is sheer bunk, but I’m going to switch off my skepticism for a while so I can enjoy the ride.”

But that’s not how it works. We don’t will our suspension of disbelief. If the story is strong, if the teller has craft, our suspension of disbelief just happens to us, with or without our permission. Chalk it up to the power of emotion. Successful stories generate powerful feelings, and strong feelings act as a solvent on our logic and our skepticism. To put it positively, good stories—fictional or not—make us more open minded. To put it negatively, they make us a lot more gullible.

This is the reason, as explained by the science journalist Maria Konnikova in her book The Confidence Game, why a powerful, emotion-drenched story is at the heart of every con job. And it’s also the reason that academic journals exclude storytelling technique from scientific reports.  Scientists understand that storytelling dials up emotion and dials back rationality, clouding objective analysis.

When John Carreyrou’s first exposé was published in The Wall Street Journal, Holmes appeared on CNBC’s Mad Money to control the damage. “This is what happens,” she said, “when you work to change things, and first they think you’re crazy, then they fight you, and then all of a sudden you change the world.” Holmes was desperately struggling to reestablish herself as a heroic striver beset by shadowy antagonists (the “they” of her formulation). After all, what kind of story would it be if the heroine had no hardships to surmount or villains to defeat?

But Carreyrou continued to report, eventually seizing primary authorship of the Theranos story. And this still-evolving narrative must feel, to Holmes, a lot like a Greek tragedy—with the hero rising high and crashing hard due to the sin of hubris. On the other hand, the general public probably reads the Theranos narrative like one more made-for-Hollywood story about a corrupt tech megalomaniac. (In fact, Holmes is set to be played by Jennifer Lawrence in a film written and directed by Adam McKay of The Big Short.)

But business professionals should read the story of Theranos as a cautionary tale that carries at least two big lessons. First, while it’s true that individuals and organizations need to cultivate storytelling craft, they also need to prepare their defenses against cheats and manipulators. While stories often provide symbiotic benefits to teller and receiver, we must remember that they are told mainly in the teller’s interests. We humans are—by our deepest natures—suckers for story. With apologies to Coleridge, not suspending disbelief is what requires an act of will.

Second, a real and seemingly permanent culture of business storytelling is emerging as books on the subject proliferate, as entrepreneurship programs introduce storytelling into their curricula, and as companies employ Chief Storytelling Officers. The Theranos debacle shows how important it is to build this culture on a rock-solid ethical foundation. Now is the time to acknowledge how tempting it can be to deploy story—as con artists do—as a weapon of psychological and emotional manipulation.

Establishing a culture of honest storytelling is not only a moral imperative for companies and workers, it is better business in a long-term, bottom-line sense. No matter the genre or format, the ancient prime directive of storytelling is simple: tell the truth. This applies even to the fantasy worlds of fiction. “Fiction,” as Albert Camus put it, “is the lie through which we tell the truth.” The world’s greatest storytellers don’t eschew falsehood and inauthenticity because they are morally superior to the rest of us (anyone who’s read around in their biographies knows this is not the case). They do so in recognition that truth-telling is better business for them as well.