For two decades, well before the five Inside Out emotions scrambled for dominance in the brain of an 11-year-old girl, Pixar has been making movies about the messy feelings associated with growing up. The inevitable bittersweetness of bidding farewell to childhood has been a prominent theme in at least a third of the studio’s work by my count, including the Toy Story movies, Monsters, Inc., and Finding Nemo. So what makes Inside Out—widely lauded by critics as a masterpiece that sets a new bar for animated creativity and emotional resonance—such a noteworthy portrait of what happens to the heart and mind as the body matures?

For starters, while previous Pixar movies have offered poignant reminders that navigating the milestones of kid-dom can be messy and painful, Inside Out essentially makes that fact its plot. The journey into young Riley’s mental circuitry doesn’t just touch on the psychological impact of coming of age, it focuses entirely on that subject, turning the subtext of other Pixar films into actual text. Director Pete Docter and his team also probe the human mind in a way that’s rooted in actual science, yet they illustrate that science with the sort of bold imagination usually reserved for Caldecott Medal-winning children’s literature. According to Inside Out, the middle-school-girl brain is simultaneously orderly yet fragile, crowded with highly charged voices (some previously heard on NBC sitcoms, The Daily Show, and/or Saturday Night Live), and aesthetically similar to a pinball machine, a Lite-Brite, and multiple levels of Candy Crush. It’s rare in a children’s film—or for that matter, any film—to see elements of the human nervous system rendered with such exquisite care and unmitigated glee.

But the film’s point of view is more important than its plot, or its sophisticated view of the machinations behind Riley’s meltdown. For the first time, a Pixar film is confronting how much it hurts when a child realizes her childhood will end—while it’s still ending. It literally gets inside her head, then bluntly announces that being a kid hurts because it doesn’t last. That feels refreshingly candid, even for Pixar.

Pixar’s artists are known for many things, including their pioneering work in computer animation, and having wonder emporiums for offices. They’re also known for frequently making audiences cry, usually by pressing on the parts of our hearts that got permanently bruised during the bumpy ride out of our formative years.

The first Pixar feature that firmly, unapologetically stuck its thumb right on one of those bruises was Toy Story 2. Before I can even type “Sarah McLachlan,” you probably realized which scene I’m thinking about: the one where Jessie recalls the heartbreak of being left behind by Emily, her original owner, while McLachlan sings “When Somebody Loved Me” to underscore the moment. It’s physically impossible for me to watch even a few seconds of that sequence without tearing up, and I know, because I’ve tried at least 20 times. The marriage of McLachlan’s vocals—which, science has proven, induce quiet weeping in the same way that Pavlov’s ringing bells cause dog-salivation—with all that wrenching imagery of a content-then-bereft Jessie jams a stubbornly immovable lump in the throat. But that’s not why many of us cry during that sequence. We cry because it reminds us of how easily we abandoned the toys we had as children. We cry because it reminds us that kids move on and stop being kids, something that’s already happened to us and may be happening, right now, to our own children.

We realize all of that through Jessie, a plaything who feels the profound ache associated with growing older, but only by watching that transformation occur in someone else. “You never forget kids like Emily or Andy,” Jessie ruefully tells her new pal Woody, referring to Woody’s beloved original owner as well as her own. “But they forget you.” As for Emily, she seems too busy trying out makeup with her pre-teen besties to reflect on what she’s leaving behind when she dumps that plucky cowgirl in a donation box.

In the Pixar movie that immediately followed Toy Story 2, 2001’s Monsters, Inc., little pig-tailed Boo also reaches a point where she has to move on without her favorite play-buddy, Sulley. But again, just as in Toy Story 2, the pain that accompanies that milestone is felt more deeply by Sulley than by the giggly little girl inching, in tiny increments, closer to adulthood.

In the moving goodbye scene between the two, Boo is sad when she realizes her “Kitty” is leaving, but she clearly doesn’t process the implications of the departure. As soon as he exits her room, she scampers over to her closet, yanks open the door, and shouts “Boo!” fully expecting to see that John Goodman-voiced pseudo-yeti standing there. Sulley and Mike, though, understand exactly what it all means. “Go ahead,” Mike tells Boo just before Sulley ushers her into her toy-strewn room for the last time. “Go grow up.” (The end of the film, in which Boo’s door is fully restored and Sulley once again enters her world, admittedly softens the finality of Sulley’s farewell, suggesting that while he and Boo can’t return to the happiness they shared during her time in Monstropolis—read: her most innocent, childlike days—they can at least occasionally visit.)

This same relationship construct—a child matures while a grown-up watches wistfully from the sidelines—plays out in Finding Nemo. During his trip to 42 Wallaby Way and back, Nemo becomes increasingly conscious that he’s getting older and more self-reliant, but that realization excites him. He may mourn the loss of his mother and the temporary absence of his father, but the clownfish with the wonky fin is never emotionally conflicted about the prospect of having new adventures and growing older. All the sorrow and grief surrounding that transition belongs to Marlin, the overprotective father who eventually learns to let his son swim in his own current. ” “Go have an adventure!” Marlin shouts supportively after Nemo in the movie’s final scene. But as soon as his boy is out of earshot, he quietly adds, “Goodbye, son.” It’s impossible not to hear the heartsickness in that whisper.

Up—co-directed, like Monsters, Inc. and Inside Out, by Pete Docter—shows a man dealing with the finality of his own youth. He’s just doing it long after his youth has ended. Yes, technically, the 10th Pixar feature is about an old man soaring to Paradise Falls as a tribute to his beloved late wife. But because Carl and Ellie first planned their epic South American exploration when they were kids flipping through the pages of Ellie’s Adventure Book, Carl’s journey in Up can be interpreted as not just his goodbye to Ellie, but a final embrace and subsequent release of his boyhood. However, because Carl is a senior citizen, he obviously has some distance from the acute pain a child experiences when he first feels what it’s like to graduate from kidhood.

Pixar narrows that gap a little in Toy Story 3, in which Andy reaches college age and finally, like Toy Story 2’s Emily, puts Jessie, Buzz Lightyear, and the rest of the gang in a box to be donated. But unlike Emily, he ultimately doesn’t just dump the box on the side of a road; he hands it off to young Bonnie, the next generation of caretaker for his married potato-heads and evil piggy bank. That toy-torch-passing—particularly Andy’s reluctant decision to finally give up Woody—is poignant and significant because this time, both Andy and his secretly animate buddies know this event symbolizes the end of Andy’s wonder years. Again, though: Andy is having this realization as a young man heading off to university life, not a kid still grappling with the day-to-day awkwardness, confusion, and joy—and Joy!—of trying to cross that bridge to adulthood.

Which finally brings me to Inside Out, where the central premise, about a sixth-grader trying to cope after moving from Minnesota to San Francisco with her family, may be Pixar’s simplest and most relatable to date. In Inside Out, Riley’s parents are concerned about what’s happening to their daughter when her mood swings becomes more erratic. But the film isn’t about their feelings. It’s also not about Riley being awash in nostalgia for a childhood she left behind long ago, à la Andy in Toy Story 3. Here, there’s no longer any distance between the child going through significant changes and the person processing those changes—they are one and the same. To borrow from the David Bowie song that’s also quoted in the opening of The Breakfast Club: Riley eventually becomes aware of what she’s going through.

Before she can reach that point of awareness, though, Riley literally loses some of her marbles, in the form of core long-term memories—which, as drawn by the Pixar team, resemble marbles with the touch-and-swipe functionality of an iPad—that get excised from or altered in the deepest recesses of her mind. Two key moments in Inside Out ultimately allow Riley to confront her post-move agony and acknowledge, for the first time, life’s harshest truth: that nothing in it stays the same. The first is classic Pixar. The second demonstrates what makes Inside Out different from every other Pixar film that came before it. (By the way, this is where the spoilers get extra-spoilery.)

After getting sucked out of the central control room in Riley’s brain, Joy and Sadness meet Bing Bong, Riley’s imaginary friend from early childhood. Riley rarely thinks about Bing Bong anymore, which prompts the walking mash-up of multiple Dr. Seuss characters to cry candy tears that make him look like a depressed elephant piñata. After Joy and Bing Bong fall into an abyss and are unable to give Bing Bong’s wagon enough momentum to catapult them out, Bing Bong decides to sacrifice himself so Joy can escape and survive. By erasing himself from Riley’s memory, he leaves Joy unencumbered enough to make the trip out of that mental hole.

The message in all this: To move forward as well-adjusted adults, we must set aside some childish things. In that context, Bing Bong is a purely Pixar creation. He’s what forgotten Jessie was for Emily in Toy Story 2, what Sulley was for Boo in Monsters, Inc., and what Woody, Buzz, and the rest were for Andy in Toy Story 3: once-beloved friends that at some point lose their active place in the heart. In those previous movies, the harshness of those ruptured relationships was mitigated by the fact that we got to see those toys and monsters continue living, with other owners or in their respective universes. Inside Out is more honest. When Bing Bong goes, it’s clear he’s never coming back.

The death of that imaginary pal is a necessary precursor to the development that leads to Riley’s epiphany: the reconciliation between Joy and Sadness. Throughout much of Inside Out, Joy shoves Sadness aside, believing that every time Sadness touches one of Riley’s marble-memories and gives it a tinge of blue, she’s ruining everything. It makes perfect sense that, with that pixie haircut, green dress, and ever-present glow, Joy looks a lot like Tinker Bell, fairy cohort of Peter Pan, the Boy Who Wouldn’t Grow Up. What is “not growing up,” if not a stubborn belief that everything will always work out in your favor, that there’s nothing to experience but joy?

Eventually, in another moment that will cause 3-D lenses to get misty, Joy sees that in many of the supposedly purely happy Riley memories, melancholy and disappointment were present, too. Light can’t exist without dark: It’s something most grown-ups know, but when Joy finally understands this, it feels as though we olds are really getting it for the first time, too.

After Joy and Sadness return to headquarters and start running the controls in Riley’s brain as a team, the young heroine finally breaks down in front of her parents and confesses how undone she’s been by leaving her Minnesota home. She realizes she doesn’t just miss her old friends, she misses what the place represents: the comfort and security of being little. She knows she can’t go back to Minnesota, and she can’t go back to being a kid. Her parents are there to comfort her when that understanding hits, but even so: This is a moment that hurts. This is Pixar—and, by extension, Walt Disney Pictures—announcing to multiplexes full of children that their childhood experience is going to end soon, and that it’s going to suck. As I’ve noted here, Pixar has hinted at that idea before. But now the filmmakers are just saying it, without cushioning the blow.

It’s unclear how young moviegoers, who rarely see movies made for their age group that invite this much introspection, will respond to such a straightforward attempt to address the emotional baggage they carry. Some early reviews have suggested that Inside Out may be better received by adults than the summer-camp set. All I have to go on is the reaction of my own son, who is three years younger than Riley. When Inside Out ended and the credits began to roll, he sat in his seat, seemingly struck mute. I asked if he liked the movie, but he didn’t want to talk. When we started to drive home, I asked again: “Did you like the movie?” Finally, he conceded it “had too much sadness in it.”

Of course, two days later, when I mentioned Inside Out again, he said he loved it, and proceeded to crack himself up by reliving the moments when flame-headed Anger came dangerously close to saying cuss words.

Clearly Anger and Joy are the ones running his controls right now. That’s okay. He’s 8. But when he gets closer to 11 and starts to see tinges of blue creeping into his memory-marbles, I’ll be glad all over again that a movie like Inside Out exists, to acknowledge that growing up means giving Sadness a chance to be in charge, and that when that happens, it’s totally okay.