Why does Nicole (Scarlett Johansson) love Charlie? He’s steady. He’s a great dad to their 8-year-old son Henry. He’s a good cook, and the caring head of the avant-garde theater company that employs both of them—he the director; she his lead actress. Why does Charlie (Adam Driver) love Nicole? She gives thoughtful, perfect presents. She’s a great mom, “a mother who plays, who really plays.” She’s every bit as competitive as he is. And she knows when to push Charlie to be a better man.

Then the montages and voiceover come to a screeching halt. These lists, complemented by a slew of romantic, incomplete images arranged into a slice of Nicole and Charlie’s life, were an assignment, a task given to the couple by their mediator. Nicole, embarrassed, can’t even bring herself to read her list aloud. Theirs is not an everlasting love, even if we can hear the faint echoes of a union promised to withstand a lifetime. Within its first 10 minutes, Noah Baumbach’s “Marriage Story” has more emotional weight than most movies can muster over their entire runtime.

So what happened? As Nicole leaves New York to film a television pilot, and Charlie gears up to bring their play to Broadway, the distance between the couple increases exponentially. Now, instead of sleeping in separate beds (well, Charlie’s been sleeping on the couch) and occupying opposite sides of the same subway car, there’s an entire country separating the two. While on the west coast, Nicole hires lawyer Nora Fanshaw (a fabulous Laura Dern), the first step in her search for what she actually wants.

“Forced” to find representation of his own, Charlie descends into a maddening spiral, as he attempts to keep partial custody of Henry. He’s a better husband in divorce, it turns out. Dismantling Charlie’s selfishness with a painful precision, “Marriage Story” makes very clear that we are the architects of our own destruction—legally binding pieces of paper or not. Still, Baumbach finds some perverse fun in his examination of the bureaucratic labyrinth two must navigate when settling and closing a marriage. Separating was never going to be easy. But does it have to be this hard?

It’s a topic the filmmaker has given considerable thought, having already explicated divorce with “The Squid and the Whale” back in 2004 and experiencing divorce himself in the time since. (Baumbach says his ex-wife Jennifer Jason-Leigh “likes it [‘Marriage Story’] a lot,” a tidbit only relevant because I find it hilarious.) Here, Baumbach—a master of montages like the one that opens the film—slows down, a smart choice that allows both the material and his collaborators room to breathe.

Driver’s uncanny ability to embody both masculine assurance and deep sensitivity—simultaneously—has made him one of the most impressive actors of his generation. Still, he’s rarely been put to better use. Driver’s playing a person in some ways defined by his egotistical delusions, yet there is still something sympathetic in his movements. We don’t spend as much time with Johansson’s character, and while the actress has been saying some really dumb stuff in public lately (defending Woody Allen, proclaiming “I should be able to play any person, tree or animal”), her work here is just as engaging. These people are out of sync: Nicole’s deep into her suffering when we meet her, with the film charting her re-emergence; Johansson humanizes a person learning to prioritize herself for the first time in years.

Of course, even as Charlie and Nicole move in different directions, their collision is inevitable. It happens inside Charlie’s barren, new apartment, an argument so fierce it leaves a mark—on both the setting and the viewer, not to mention the characters. The scene—along with an awkward sequence in which Charlie is served his divorce papers—is reminiscent of the extended slapstick set-piece in Baumbach’s “Mistress America,” and further proof this writer/director is the closest we’ve got to an old-fashioned comedy-drama auteur like Preston Sturges.

But again, the real secret to “Marriage Story’s” success is that Baumbach has stripped back his approach—this film never gets in its own way. This is about Charlie and Nicole, just two people. We get in their heads, learn how they think, why they’re hurting and why they’re hurting each other. While it’s fitfully funny, this is a movie for adults, in all its maturity and nuance and careful rejection of vindictiveness. I daresay the average Brandeis student has not experienced the end of a relationship like the one on-screen; maybe in a decade I’ll have lived through a breakup like this. That Baumbach has been able to capture such a staggering reality is nothing short of astonishing.