The year 2020 was a bad one for Cassie Phillips. Her husband had recently returned from an overseas deployment, and while he was away, she told me, she’d rarely heard from him. The pandemic began, and the family moved to Savannah, Georgia, where they didn’t know many people.

Phillips felt isolated in her new home, and her marriage was falling apart.Late at night, on her computer, she started writing out some lines—“If they want to go weeks without talking to you, LET THEM”; “If they want to follow the crowd, LET THEM”—to remind herself that she couldn’t control her husband’s behavior. The writing was an attempt to “get through the day knowing I didn’t have anybody but myself,” Phillips said; she was “learning not to give up on other people, but understanding I had to trust myself.”The phrase Let them wasn’t entirely Phillips’s own invention—she was inspired, in part, by a video clip in which Tyler Perry’s character Madea says, “If somebody wants to walk out of your life, let them go.” In 2022, Phillips left her husband and got the words let them tattooed on her arm, with the L in print and the rest in cursive.

She posted a picture of the tattoo on Facebook, along with the lines she had been writing—she calls them a series of mantras, but many people refer to them as a poem. That post went viral, for a poem at least; currently, it has nearly 50,000 shares.Phillips saw people reposting the poem on Facebook and Instagram, and even screen-printing it on T-shirts. She thought that was cool, but it didn’t occur to her to try to make money from the “Let them” idea.

At the time, she was working at a nursing home and as a bartender, taking care of her kids, and trying to hold it together psychologically. “I was in survival mode,” Phillips said.[Read: This influencer says you can’t parent too gently]In May of the following year, Phillips saw an Instagram video from the popular podcaster and self-help author Mel Robbins in which Robbins said, “I just heard about this thing called the ‘Let Them Theory.’ I freaking love this. If your friends are not inviting you out to brunch this weekend, let them.” Initially, Phillips, who assumed the post was referring to her work, was flattered; she sent Robbins a message thanking her for sharing her words.“I didn’t really care about credit,” Phillips said.

She didn’t know what Robbins had planned for the theory. “I didn’t really think it was going to be”—she searched for the right word—“kept.”A few weeks after Robbins posted her Instagram video, she talked about “Let Them” on her podcast, which has more than 37 million monthly downloads. “I shared something called the ‘Let Them Theory’ in an Instagram post less than a week ago, and I just looked it up; there are over 14 million views of this thing,” she said.

The reason the post resonated, she added, is that “every single one of us struggles with controlling behavior, or we struggle with controlling thoughts, and the ‘Let Them Theory’ is a way that you can check yourself so that your controlling nature or your controlling or obsessive thoughts don’t control you.” The YouTube video for that episode now has more than 3 million views.In late 2024, Robbins released a book called The Let Them Theory, which became the best-selling book of 2025 and has sold more than 9 million copies. As her publisher put it, “I’ve been working at Hay House for 37 years, and we’ve had lots of big-selling books, but nothing as big as this.” Robbins released the book into a marketplace where nonfiction sales—never especially robust—were particularly abysmal, down nearly 10 percent from the previous year.The Let Them Theory advises readers to stop trying to control others and instead take responsibility for themselves.

I found parts of it genuinely helpful. Robbins includes one of the best explanations of motivational interviewing—a technique in which a person tries to help a loved one come up with their own reasons for changing their behavior—that I’ve read in my 12 years of covering psychology. And I appreciated her advice to not force a friendship.

Still, reading the book, I found some tonally jarring clunkers. A chapter arguing that people should accept that life isn’t fair includes the line “It’s not fair that your country is torn apart by war.” At times, she assumes that her audience has the worst possible habits and intentions: In assuring the reader that they can “create anything you want in life,” Robbins adds that they are unlikely to do so if they keep up “this stupid and toxic habit of comparing yourself to other people. Stop it.” The book is definitely motivating, in the way that getting yelled at by your mother can be motivating.Robbins writes that the theory came to her when, on the night of her son’s prom, her daughter Kendall urged her to stop micromanaging his choice of pre-dance restaurant.

“Mom, if Oakley and his friends want to go to a taco bar for pre-prom, LET THEM,” she recounts Kendall saying. Robbins also acknowledges that many peop