A woman in glasses with her hair pulled to the top of her head looks over a book that she is holding open. There is a caption at the top of the photo that says “They may be characterized as ‘old souls.’” Amber Nuño is one of the many social media users who deeply connected with the book “Adult Children of Emotionally Immature Parents” by Lindsay Gibson.Credit...Amber Nuño

In 2021, Amber Nuño was living in Los Angeles, working at her dream job developing new products at Apple, making six figures and driving a nice car. On the surface, her life looked perfect, but she still felt deeply unsatisfied for reasons she couldn’t understand.

“I felt like I should be way more appreciative,” Ms. Nuño said in an interview. “I should be happier. Why am I not happy?”

While browsing Amazon one evening, she came across the self-help book “Adult Children of Emotionally Immature Parents: How to Heal from Distant, Rejecting or Self-Involved Parents,” by Lindsay Gibson, and decided to start reading it. A few pages in, it hit her: Ms. Nuño, who was living with her mother at the time, realized she was unhappy “because of the way the relationship with my parents was so strained.”

With the help of a therapist, Ms. Nuño began diving deeper into the book, and noticed more and more parallels between what Dr. Gibson described and her own experiences.

Published in 2015 by New Harbinger Publications, a small press in Oakland, Calif., the book is an attempt to help readers understand strategies for better dealing with parents whom Dr. Gibson deems “emotionally immature” — those who refuse to validate their children’s feelings and intuition, have difficulty regulating their emotions and may be reactive, inconsistent and lacking in empathy or awareness.

In Dr. Gibson’s research, this kind of parent-child dynamic tends to lead children to grow into adults who are emotionally shut down, lack confidence and tend to isolate.

“This book helped me rationalize and kind of observe my mother a little more neutrally,” Ms. Nuño said. “It gives you those ideas of how to observe more neutrally and objectively versus being stuck in the dynamics of it all, getting triggered and upset.”

Not long after she started reading the book, Ms. Nuño moved out of her mother’s house and into her own apartment and recorded a TikTok video about the book, which she said made her question her whole life. As other fans of the book began to fill her comments section, Ms. Nuño realized she wasn’t alone.

“Adult Children of Emotionally Immature Parents” has become one of the most popular self-help books regarding parent-child relationships, selling more than 1.2 million copies and spending six weeks on the New York Times best-seller list last summer. And though it was published nearly a decade ago, and was originally marketed to psychologists, it has recently found a surprising community of fans on social media, who talk about how the book has fundamentally altered their view of parental relationships. Image The book cover for “Adult Children of Emotionally Immature Parents: How to Heal from Distant, Rejecting, or Self-Involved Parents.” It shows paper cutouts of a family on a tabletop. The book, which was originally marketed to psychologists, has sold more than 1.2 million copies thanks to Dr. Gibson’s popularity on TikTok.Credit...New Harbinger Publications

Clips of people reading passages of the book receive millions of views on TikTok, and the title has become so ubiquitous online that it got the meme treatment and was on the “Want to Read” list on a Goodreads page that appears to have belonged to Luigi Mangione, a man who has been charged with murder in the killing of the chief executive of UnitedHealthcare.

The book’s rising popularity comes at a time when young people may be feeling especially estranged from their families — politically, emotionally, generationally — and are searching for answers to explain why.

“It caught the wave,” Dr. Gibson said in a recent interview about the book’s surge in popularity. “There has been a swell building on this, giving people permission to pay attention to their internal experience. And I think that my book came along at a time when people were open to really reassessing their interpersonal realities.”

“People are no longer willing to have somebody invalidate what they know deep down,” she added, “and when they find a book or a way of thinking that confirms something that they knew, it’s a paradigm shift, and it’s life-changing.”

Dr. Gibson’s publisher confirmed that sales have spiked since 2020, with the largest volume occurring in 2023, “thanks to Gibson’s fans on TikTok.”

The book is a result of Dr. Gibson’s almost 30 years of work as a clinical psychologist, during which she noticed a strange pattern among her patients, many of whom came to her for help improving their relationships with their parents. Though her clients were willing to be fair, insightful and introspective, she said, their parents were not.

“They were dealing with these people who didn’t self-reflect, who were extremely egocentric, who just had very little empathy for what my client was going through,” Dr. Gibson said. “They would deny problems and refuse to communicate, and then they would expect my client to build up their self-esteem and emotionally stabilize them.”

For Dr. Gibson, the conclusion was obvious.

“Wait a minute,” she realized. “All the wrong people are in therapy.”

When she began using this framework in her sessions with clients, “it was a very, very helpful concept for them,” she said. “Like, Well, maybe I’m reacting normally to what is poor treatment from people who can’t be empathic or considerate of me as another human being — and that is a paradigm shift. When that happened, my client really began to get their self-confidence back. They began to know themselves better. And they really got released from this fear and shame and guilt and self-doubt that they had trying to figure out how to handle these very difficult people.”

“It caught the wave,” Dr. Gibson said in a recent interview about the book’s surge in popularity. “There has been a swell building on this, giving people permission to pay attention to their internal experience.”Credit...New Harbinger Publications

In short, Dr. Gibson’s book gave them permission to say: It’s not me; it’s them.

Of course, not everyone has emotionally immature parents, though a cursory glimpse of conversations about the book on social media might have you thinking otherwise.

“I was just shocked,” Ms. Nuño said when she realized just how many people on TikTok seemed to relate to the book. “I know there are lots of parents and dynamics out there that maybe aren’t the healthiest, but I didn’t realize so many of us were dealing with people who aren’t working through their own traumas, and then raising adults to be living in the same cycles.”

Now, a growing number of people — including Ms. Nuño — have chosen to go “no contact” with their parents, a phenomenon that the clinical psychologist and author Joshua Coleman told The New Yorker was because of “changing notions of what constitutes harmful, abusive, traumatizing or neglectful behavior.” His book “Rules of Estrangement: Why Adult Children Cut Ties and How to Heal the Conflict” could be seen as the foil to Dr. Gibson’s. One chapter is given the slightly mocking subhead “My Therapist Says You’re a Narcissist” and argues that “therapists’ perspectives often uncritically reflect the biases, vogues and fads of the culture in which we live.”

Dr. Gibson doesn’t believe those arguments hold water.

“The idea that you create a syndrome, and then everybody starts coming down with it — I think it’s erroneous in this situation,” she said.

“I don’t think it’s more widespread now,” Dr. Gibson said. “All you have to do is look at the history of the world. All you have to do is read the news. That emotional immaturity, the impulsivity, the lack of regard for other people’s feelings, the egocentrism, the lack of self-reflection: It’s rampant, it’s what starts wars, it’s what causes conflicts.”

For people like Ms. Nuño, the book has been a lifeline.

“I found community,” she said of the others online who also connected with the book. “For the longest time I felt like, Wow, I really don’t like my parents. I didn’t love them in the way people did, and it was because of how they treated me. And I felt like that was taboo my entire life. But with all the comments of support I started to feel like, Wow, I’m not the only one out there who feels really complicated about their parents.”