As Mel Robbins tells it, the concept for her new self-help book, “The Let Them Theory,” came to her on the night of her son Oakley’s junior prom. Overcome by the realization that her youngest child would soon be leaving her, Robbins coped by micromanaging the scene. She pressured Oakley to give his date a corsage. Fretted about the weather. Worried that the teenagers hadn’t made a dinner reservation.

Fed up, her daughter Kendall finally snapped: “Mom, if Oakley and his friends want to go to a taco bar for pre-prom, LET THEM,” Robbins writes in the book. If they get hungry? Let them! Soaked? Let them! Let them, let them, let them.

This mantra of radical acceptance was instantly soothing to Robbins, who — by dint of her iron will and innate confidence — has emerged as one of social media’s go-to motivational influencers (a term she loathes, incidentally). Robbins began repeating it whenever she felt stressed about other people’s thoughts or actions. In May 2023, her minute-long video about the term took off on social media; some of her followers even got “let them” tattoos.

“Let them” is not the first time Robbins, 56, has spun a catch phrase into content gold. She shot to fame more than a decade ago with her “five-second rule,” the idea that whenever you feel an impulse to act on a goal — whether something small, like getting out of bed when the alarm goes off, or big, like finally giving notice at work — you simply count down: 5, 4, 3, 2, 1, then go! Do it. (The TEDx talk in which Robbins debuted that particular hack has been watched more than 33 million times, and she turned it into her first best seller.)

“There is an obsession with being smart, I think, in the thought leadership space,” Robbins said when we met in November at the loftlike headquarters of her media production company in Boston’s seaport district. “And I would rather be useful.”

If Robbins looks familiar, with her bright blond hair and signature dark-rimmed glasses, the algorithm may have sent you one of her pithy takes on life’s problems — like how to stop trying to “fix” your parents, or her frequently memed exhortation against spending money on stupid … stuff. Maybe you saw a recent video of her — clad in a sports bra and hot pink hair rollers — weeping about her recent sit-down with Oprah Winfrey, who declared “The Let Them Theory” one of the best self-help books she has ever read.