This post contains sad spoilers for Inside Out.

Yeah—like pretty much everyone else this weekend, I cried during Inside Out. But for me, the moment in Pixar’s new masterpiece that hit hardest wasn’t Riley’s return to her parents, or the disappearance of Bing Bong, or any of the movie’s other overtly heart-tugging scenes. Instead, it was a moment early in the movie, in which 11-year-old Riley—tucked uncomfortably into a sleeping bag on the bare floor of her new San Francisco house—gets kissed goodnight by her mom. “Through all this confusion,” her mom tells her, “you’ve stayed our happy girl.” Riley’s father is very worried about work, she notes, so “if we could keep smiling, it’ll be a big help.”

It’s a throwaway scene on its surface—and yet sitting in the theater with my two daughters, I was struck right to the heart by that line. The lesson to stay positive and project happiness is one I’ve heard coming from my own mouth more than once, especially when my kids are upset by a particularly bananas period in my or my wife’s job. Since seeing Inside Out, I’ve started to reconsider the way I talk to my kids about these emotions. That’s because this children’s movie’s treatment of sadness—the emotion itself and the character of Sadness, voiced by the great Phyllis Smith—is outstanding and, I think, quietly revolutionary in its own way.

“Aren’t you a little bundle of joy?” Riley’s dad asks his infant daughter in her first moments of life. Indeed, for the first years of her life, Riley’s defining characteristic is joyfulness, as depicted in the movie by Joy (Amy Poehler)—the wide-eyed, blue-haired chief of headquarters, where the five anthropomorphized emotions work together to manage Riley’s feelings from minute to minute. The other emotions, Anger, Fear, Disgust, and Sadness (Lewis Black, Bill Hader, Mindy Kaling, and Smith), look to Joy for leadership, because there’s no situation so scary or upsetting that Joy can’t find a way to turn it around and find the happy. Indeed, much of the energy of the movie’s first act comes from Joy’s often frantic juggling as she finds ways to turn every one of Riley’s frowns upside-down.

But the move from Minnesota to San Francisco upends Riley’s emotions, and soon Joy is pushed to her limit. In a pointed scene the morning after the good-night kiss, Joy instructs each of her co-workers on their tasks to make sure Riley has a great first day at her new school, but she’s stuck on how Sadness can contribute. Eventually she draws a chalk circle on the floor of headquarters and tells Sadness to stand in it. “Make sure all the sadness stays in the circle,” she says, desperately chipper. “Doesn’t that sound fun?” It’s an echo of Riley’s mom’s gentle message of repression from the night before, and it doesn’t work—soon Sadness, unable to stop herself, has touched an important memory, turning it from happy to sad permanently. Joy is shocked and upset, and her response is a sign of Inside Out’s complicated relationship with its bright gold main character—and the little girl whose emotions it’s exploring.

Joy realizes the error of this approach in a series of sequences that are perfectly pitched to make their lesson clear to both grown-ups and kids. The most important one takes place after Bing Bong (Richard Kind), Riley’s imaginary friend, sees several set pieces of Riley’s youthful imagination (a candy house, a stuffed animal museum) demolished to make room for more grown-up fancies (like a make-believe boyfriend). Bing Bong is despondent about his own approaching obsolescence, but Joy tries to cheer him up, in a moment that will strike a chord with many parents. “Hey, it’s gonna be OK,” she chirps. “We just need to fix this! Here comes the tickle monster!”

But it’s Sadness who knows, instinctively, how to treat Bing Bong. “I understand,” she says quietly, sitting next to him. “They took something that you loved. That’s sad.” Joy looks on, irritated, as Bing Bong sobs on Sadness’ shoulder—but then Bing Bong sniffs, wipes his eyes, and feels a bit better. “How did you do that?” Joy asks Sadness, bewildered. Her entire existence, up until now, has been focused on eliminating, or at least minimizing, negative emotions; it’s never dawned on her that Sadness has a role to play, too.

That’s a potent lesson in a children’s movie, especially one with a girl at its center. After all, the emotional messages of most entertainment for kids are pretty relentlessly positive: Love your family, stay true to yourself, keep positive, never give in to despair. As the research of Stanford’s Jeanne Tsai has shown, one of the emotions that Americans in particular privilege is joy—excited pleasure. Children see around them, in books and movies and advertisements, exemplars of delight at growing up. “That makes it harder to grapple with sadness,” University of California, Berkeley psychology professor Dacher Keltner told me. “It’s a vacuum in our culture.”

But, points out Keltner, who consulted with Pixar’s Pete Docter on the film, sadness is a powerful tool, a trigger that sends kids back to their parents for comfort and connection. “You gotta hang on to that sadness,” he told me, because in the tumult of early adolescence, it’s the thing that can bring parent and child back together.

Near the end of the movie, Riley seems to be suffering from a bout of depression—aspects of her personality have fallen away, and the control board in headquarters has faded to gray, suggesting she’s gone from feeling too many emotions to feeling none at all. It’s Sadness, with Joy’s blessing, who takes over the console and brings it, and Riley, back to life—not through a tickle fight, or a game, but through an honest outpouring of true sadness. “You need me to be happy,” Riley cries, held tight in her parents’ arms, “but I want to go home.” In Inside Out, big girls do cry, and that’s OK—even necessary.

Joy, it turns out, is no heroine, though the movie cannily presents her as one at first. She’s our shiny and sweet narrator, and she clearly loves Riley with all her heart. In fact, the movie’s sophisticated narrative structure encourages us to cheer for Joy even as it gradually becomes clear that what Riley needs most —what all children need most as they grow older—is for Joy to fail. Not every moment of Riley’s life can be exultant. Not every memory in Riley’s banks should be uniformly joyful, or uniform at all: Part of growing up, the movie reminds us, is gaining access to more complicated, multicolored emotions. And so for Riley to be healthy and happy—truly happy, not “joyful”—Joy needs to shed her aversion to Sadness, the co-worker she understands the least, and embrace the role that even negative emotions have to play in a truly good life.

“I just wanted Riley to be happy,” Joy says at her lowest point in Inside Out. That happiness is all most of us truly want for our kids. Like Finding Nemo with its message of letting kids free to have their own adventures, Inside Out seems to be delivering a lesson not only to its young viewers, but to the parents who accompany them. I’m trying to embrace that message, too. When my kids have come to me sad or upset since we saw Inside Out, I’ve tried to do a better job of listening to their feelings—of trying not to solve their problems or gloss over them but to understand them, even for a moment. It’s hard! It reminds me not only of how much it hurts to see my children sad, but how much energy I spend on my relentlessly positive attitude, even when it might not be the best thing for me or those around me. I’ve been reminding myself of little blue Sadness, with her turtleneck and round glasses, lying on the floor of headquarters, crying with both deep despair and deep satisfaction. “Crying,” she says, “helps me slow down and obsess over the weight of life’s problems.” But as Keltner told me, that can be a useful moment, not a hopeless one: “Sadness,” he said, “stops the body and gets you to reflect on what’s happening to you.” I hope this uncommonly wise movie has reminded other parents, as it’s reminded me, that sadness and joy can happily coexist.