There’s an inherent good-heartedness at the center of improv comedy that is either genuine and important or overly precious and twee, depending on your perspective. In a world where everyone is constantly screaming “no,” the central premise of improv is to always say “yes.” Whatever your castmate invents as his or her reality, you accept it and build upon it rather than tearing it down. Thus, in the purest and most immediate sense, you create art, together, while an audience of strangers watches.

Improv strikes me as the most high-wire and terrifying of all public art forms. It’s a potential living nightmare, one where you walk into the lights both naked and not having studied for your final exam. When it’s done poorly, there’s little else more excruciating to watch. But when it works, when everything clicks, it feels like magic: A whole new world, emerging from whole cloth, instantaneously.

Don’t Think Twice, a new comedy from Mike Birbiglia, is the first movie I’ve ever seen to look at the universe of improv and take it seriously, for better or worse. It’s a movie willing to see improv, and its artisans, as the mad, self-destructive beautiful souls they are. The film takes a group of struggling actors—all improv actors are struggling— called “The Commune” and tracks their interactions, their ambitions, their limitations, and their insecurities. The film is about the bond between the kind of people who perform without a script in front of an audience every single night. Birbiglia’s tone is gentle and warm, but it doesn’t handle these people with kid gloves. There is a self-righteousness to mastering an art form that not only won’t make you rich, it won’t even pay the bills—self-sabotage is its own high, almost by design. What makes improv fun is the opposite of what gives you a career: “No” is the world of adulthood, “yes” is the fantasy to remain a kid forever.

The leader of The Commune is Miles (played by Birbiglia), a talented performer who, for all his dedication, just doesn’t necessarily have the it required to make it beyond improv. Still smarting from a failed audition for Weekend Live years before—the film’s obvious mirror of Saturday Night Live—Miles now teaches improv classes, leads his troupe, and sleeps with women far too young and inexperienced to see through him. He’s still a good guy, though, and he’s adored by his troupe, including the wayward son of a businessman who works at a Whole Foods to support his improv addiction (Chris Gethard), a woman who’s probably more talented than everyone in the group but can’t get out of her own way (Gillian Jacobs) and her boyfriend (Keegan-Michael Key), the clear star of the group whose burning ambition ultimately results in his being cast on Weekend Live. This call to the big leagues, inevitably, causes the rest of the group to reflect on their own places in the world—and their dedication to this weird art.

The movie’s got a little too much plot, with complications involving a closing of a beloved theater and a Lorne Michaels-like character who skulks around like the angel of death. (Though I do prefer to believe Lorne Michaels is like this.) Some of the character traits feel sketched-in, as if there were only enough screen time to give everybody one thing to do—one has a sick dad, one is a cartoonist, one has wealthy parents who support her—but it gets the big stuff right, particularly in the way competitive creative people do their best to be supportive of friends who catch a big break, but who can’t help but rage internally about their own failings.

In his stand up, as well as in his storytelling on This American Life, Birbiglia is an empathetic performer. He smartly cuts against that here; he’s not a jerk, exactly, but he’s a lot less interesting in everyone else’s well-being than he lets on. But the real stars are Jacobs and Key. Jacobs, so excellent on Netflix’s Love (and, of course, Community), has a tricky assignment, having to showcase her character’s undeniable talent and also her pathological need to undercut it, for reasons that are unspoken but always present. As for Key, it’s been pretty clear for a while that he’s a huge movie star waiting to happen, and he adds some tools to his arsenal here, as the guy whose ship finally comes in and realizes, to his own dismay, that his life, and his friendships, are never going to be the same. I’m pretty sure Key can do anything. He sure does it all here.

There’s a generosity of to spirit that the film that seems to draw directly from improv, with everybody getting a turn in the spotlight. The performers never get too nasty with each other, even when they’re thinking nasty thoughts. It’s also worth remembering that the movie itself is, in fact, pretty funny: This is not a queasy cinema of squirm in which you’ll shift uncomfortably in your seat watching people fail at improv. The movie wants to ultimately give you the same high that improv, when done well, can give you. These are good people ferreting their lives away at the only thing they’ve ever done well or cared about, and the movie has unquestioned affection for them. It does such an excellent job chronicling the world of improv, in fact, that it makes an excellent case for never, ever trying it. Life is uncertain and scary without having to do it all on stage.

Grade: B

Grierson & Leitch write about the movies regularly for the New Republic and host a podcast on film. Follow them on Twitter @griersonleitch or visit