This past Sunday, Keila Shaheen woke up to find that, once again, she was the best-selling author across all of Amazon. To get there, she’d outsold every other book on the platform—including Walter Isaacson’s buzzy biography of Elon Musk and the Fox News host Mark Levin’s screed The Democrat Party Hates America. She’d even beat out Oprah.

At just 24, she is a bona fide publishing juggernaut. And yet few outside of TikTok have even bothered to notice. That’s probably in part because her best-selling book isn’t actually a book at all in the traditional sense. It’s a self-published mental-health guide called The Shadow Work Journal, and its success has been fueled by a steady drumbeat of videos posted on TikTok. Inspired by the writings of the psychoanalyst Carl Jung, it offers readers prompts and activities for interrogating the unconscious, repressed part of themselves. By getting to know our “shadow,” the Jungian theory goes, we can better understand ourselves and our behavior.

One exercise invites readers to stare at themselves in a mirror for five to 10 minutes and talk to their reflection, writing down their observations afterward. Another has them make a gratitude list. A page on “wound mapping” asks the reader to circle statements such as “hates being alone” or “struggles to let things go” in order to identify their “inner-child wound.” In one video posted on TikTok, which has more than 50 million views, a reader has circled almost all of the statements: “Realizing I have more issues than I thought,” the caption reads. I got my copy during a long trip and did one of the activities on the plane; it turned out that my shadow was tired of flying and wanted to be home.

Shaheen isn’t a practicing therapist, and her traditional mental-health credentials are limited: She graduated from Texas A&M University in 2020 with bachelor’s degrees in psychology and marketing, and took a training course in cognitive-behavioral therapy (CBT) from Achology’s Academy of Modern Applied Psychology, an online school. (Licensed therapists typically have a master’s degree in counseling, thousands of hours of supervised experience providing therapy, and a passing grade on any number of licensure exams.) Instead, Shaheen’s background is in marketing and brand strategy. She’s done this work for various companies, including TikTok itself, where she was a creative strategist. Her knack for storytelling on social media is evident in the book’s viral success: TikTok users have gone rabid over her journal. Some have raved that the workbook is “cheaper than therapy” and posted dreamy videos of themselves filling it out on a sunny day. Others accused it of being demonic and anti-religious. Still more question its legitimacy as a therapeutic tool.

Shaheen defends the book by contending that it can help people. “I firmly believe everyone deserves access to mental-health resources and the chance to embark on a healing journey,” she told me over email, arguing that tools like the journal “can often inspire individuals to seek therapy,” a route she recommends “if it’s accessible.”

Shadow Work Journal videos have passed 1 billion views in total on the platform, and many of these posts function as direct advertising thanks to TikTok Shop, the platform’s new e-commerce brand. The videos feature links to buy the journal in the app. TikTok Shop also offers affiliate features that allow creators who make videos about products to get a commission for each sale. Many of the journal videos use this feature. One 20-year-old part-time student I emailed told me she’d made about $1,000 off of her video about the book. She had requested a free copy of it through a creator program, and in exchange, TikTok prompted her to post about it.

[Read: TikTok is doing something very un-TikTok]

The rise of the Shadow Work Journal is another reminder of TikTok’s power—to generate conversation, to sell a ton of books, to keep people in an algorithmic loop indefinitely. Though it was first published in the fall of 2021, the journal reached hit status this year, after being listed in TikTok Shop. It has sold 290,000 copies on TikTok alone since April—45 percent of its overall sales, Shaheen says, meaning more than half a million sold in total. As a point of reference, Isaacson’s Elon Musk sold 92,560 copies the old-fashioned way in its first week. Shaheen sent me screenshots of four separate times she’d reached the top slot on Amazon since mid-August, including this past Sunday.  

However much they help spread the word, algorithms alone cannot explain the journal’s popularity. Americans’ struggles with mental health are well documented, particularly among young adults, who tend to spend more time on TikTok than older people. Therapy is expensive, commonly stigmatized, and at times inaccessible—many professionals say they can’t meet patient demand. People are looking for help.

That they’re finding it in an affordable, DIY solution is not surprising; self-help books have always been popular in America. That they’re doing this is also not necessarily bad. “The Shadow Work Journal can give valuable opportunities for reflection and growth,” Corey Basch, a public-health professor at William Paterson University, told me. But she also situated the book in a broader context: an era of free, sometimes questionable medical advice on social media. Basch co-authored a 2022 study that examined posts published under the #mentalhealth hashtag on TikTok. Though some legitimate therapists have found success on the platform, Basch characterized the material she’s come across as “consumer-driven and rife with issues related to credibility.” She cautioned that working through tough topics might lead a reader to “rekindle trauma,” and that experts often advise that such work be done as part of therapy with a supervising professional. The journal does come with a disclaimer: “While anyone can do shadow work, a licensed mental health expert is a good option, especially for individuals who have experienced severe trauma or abuse.”

[Read: What in the world is happening on TikTok Live?]

Shadow work, it should be noted, is a niche practice. Though it has its proponents, psychoanalysis has taken a back seat to more empirical methods. Now Google searches for shadow work are skyrocketing alongside sales of the journal. Connie Zweig, a retired psychotherapist and herself the author of books on shadow work, told me that she was “very surprised” to hear how much the topic had blown up. “It’s exciting because it can open doors for people,” Zweig told me, “but it’s also dangerous if people think this is all they need.” She thought the book had “oversimplified” the Jungian idea of the unconscious, at least based on what she’s seen of it in TikTok videos.

Joshua Terhune, a therapist in Indiana with 300,000 followers on TikTok, also had some critiques. He was curious enough to request a review copy of the journal through TikTok Shop and ended up rating it two and a half stars out of five. When I asked him if Sheehan’s CBT certificate would qualify a person to write a shadow-work journal, he laughed and said, “No, not even close.” In response to the criticism that she’s underqualified, Shaheen told me that she wondered whether critics had looked up her author bio: “If they’re not comfortable purchasing any work from an actual certified therapist, that’s okay. They can look at other options.”

She isn’t a licensed medical professional, CBT certificate or not. But Shaheen is a clear writer and an exceptionally shrewd observer of online trends. She’s struck a nerve. In one TikTok from August with 10 million views, the video’s creator extols the Shadow Work Journal for changing her life. “I wasn’t healing. My relationships weren’t successful. And it wasn’t until my shadow journal that I realized I had a lot of unresolved traumas,” she says. “This helped me call all my POWER back to me.” And yes, she’s eligible for commission.