There's a scene in Mike Birbiglia's Don't Think Twice where a character flagrantly breaks a fundamental rule of improv comedy onstage, and it's devastating. The film does such a good job making us believe in the closeness and the fragility of the group at its center that we have nothing to do but squirm when things go wrong. "Fall, and then figure out what to do on the way down," as one member quotes improv legend Del Close at the outset as having said. It's a fitting note to begin on, since so much of the movie — and of the cutthroat world of live comedy — is about the fall.

As a comedian, Birbiglia specializes in mining deeply personal and uncomfortable truths for laughs. As a director, he does the opposite, and the ease with which he is able to reverse that flow is something of a marvel. His first film, 2012's Sleepwalk With Me, was a wistful adaptation of his autobiographical one-man show in which he used his strange, inherently funny sleepwalking disorder to expose his own relationship failures. With producing partner Ira Glass still at his side, Birbiglia has now stepped out of his This American Life-friendly comfort zone for a fictional tale about a group of "yes, and" comics trying to claw their way to stardom. During the improv scenes, his camera freely roams among the performers while they conjure bits from nowhere. It's alternately hysterical and heartbreaking, comedy by way of John Cassavetes, who gets an appropriate shout-out.

The troupe, The Commune, comprises six members, all in their late thirties — the age when a particular desperation to "make it" begins to set in. Like the groups it's modeled after (The Second City, Upright Citizens Brigade), The Commune has long been a breeding ground for future stars of an Saturday Night Live-like national TV sketch show, which everyone in the improv world agrees is unfunny and yet which continues to draw eager prospects like flies to a corpse. The irony of this setup is the stuff of great character-based drama. Improv depends on a healthy group to survive, but television encourages ego and self-preservation above all else. Yet where else can a struggling improv performer hope to ascend, except in front of a camera?

Comedy nerds will thrill to the film's deft deconstruction of these worlds, but they'll be even more pleased with the casting, which is a murderer's row of funny people. The red-hot Keegan-Michael Key, of Key & Peele, is Jack, a gifted solo performer who can't stop hogging the spotlight; Gillian Jacobs (Community) is his girlfriend Sam, who fell into improv by accident and now can't imagine leaving. Key gets to show off why he's a virtuoso of sketch comedy, even busting out an Obama impression—but Jacobs had no improv experience in real life, which makes her warm, winning work here all the more impressive. "Has anyone had a particularly bad day?" she asks the audience, and in her voice is an urgent desire to right this wrong.

The other, more peripheral group members are Tami Sagher (a writer on Inside Amy Schumer)as the only performer blessed with wealthy parents; Chris Gethard (The Chris Gethard Show) as a sad-sack type who has a family crisis; Kate Micucci (one-half of Garfunkel and Oates) as a shy presence who's also a struggling graphic novelist; and Birbiglia himself as the group leader, bitter and resentful after years of watching the comics he trained pass over him on the way to bigger things. The six have an easy rapport even as unspoken rivalries simmer, as though they've been letting such tensions build on the same stage together for years.

Soon one member hits it big, though it's best not to reveal which one. What's more fascinating is how a sudden jolt of stardom creates rifts in the group, particularly when their old performing home prepares to shut down and the economic infeasibility of what they do stares them square in the face. When bad things happen to these characters, they disappear under the crutch of comedy: silly impressions, joke one-upping, and shade-throwing done under cover of a smile. But comedy can't heal everything, and when the veneer of laughter drops, it's downright ugly.

We are oversaturated with media about the hardscrabble lives of humorists, from Louie to 30 Rock to all the new streaming stuff like Difficult People (streaming shows are becoming like digital improv groups for hip comedians: a place for cachet, if not quite fame). If you're told enough times how miserable a profession is, you start to believe everyone who does it is delusional. But it's rare to see a movie or TV show grapple so delicately with the costs of success and failure in any profession, in a way that can be both specific and universal. We all want our friends to succeed, but maybe not too much.

Improv exists "in the moment," as The Commune's members frequently remind us, and it vanishes as soon as the audience goes home. The triumph of Don't Think Twice is how it reframes those moments, buries and praises them, and captures a small part of their magic for the rest of us to understand, a little better, why so many give up so much to bring them to life.

Copyright 2021 NPR. To see more, visit https://www.npr.org.