“Don’t Think Twice” depicts the travails of a longstanding improv troupe in New York City and it does so with the sort of exacting specificity only possible from a filmmaker who understands that world intimately.

That alone is not what makes the movie, which effortlessly straddles drama and comedy, and features some of the most authentic and natural acting in recent memory, such a special and noteworthy achievement.

Mike Birbiglia — the film’s writer, director and key ensemble member — has an extensive background in comedy and so the movie offers a pitch-perfect depiction of the milieu surrounding an institution akin to real-life mainstays such as the UCB Theatre or Peoples Improv Theater. It captures the spontaneity of great live comedy, the rush of performing without a script and the feel of the sort of small but avid fanbases that emerge around the regular performers at those places.

But where Birbiglia really excels is in the way he connects this particular environment to palpable emotions, especially professional jealousy, as the improv group’s star Jack (Keegan Michael-Key) lands a coveted role on “Weekend Live,” leaving behind his colleagues (including girlfriend Samantha, played wonderfully by Gillian Jacobs).

Most movies unfold along a binary emotional terrain; characters are alternately happy and sad, angry and content. Life isn’t that simple, of course. To convey the truth that many of the most important moments of everyday existence — the scenes that define us and that we’ll always remember — are tinged with complications, requires a perfect synergy between a filmmaker, his cast and the story they’re collectively telling.

“Don’t Think Twice” has many wonderful moments that collectively illustrate the truth that so much of what happens to us day in and day out, at home and at work, can’t be easily categorized on one end of the spectrum or another.

Jack, for example, learns of his “Weekend Live” audition just as fellow troupe member Bill (Chris Gethard) informs the rest of the group that his father has suffered a bad traffic accident. The actors play the scene with pinpoint naturalism and Birbiglia loads it with subtext; Key’s hesitant and uncomfortable with the timing of the good news but desperate to share it, both to be honest with his character’s friends and because of what it could mean for his future. Gethard, sitting on a couch with most of the rest of the troupe, offers a “Congrats” that’s both genuine and tinged with sadness. Birbiglia expertly cuts between them to give the actors the chance to explore the complications in the scene, and the result is that, as an audience, you feel deeply for both of them.

This is much harder to achieve than it might seem to be. The movie shows you the struggle and pain that comes with pursuing a career in the arts; it gets the inexorable pull of performing, the feeling that you are suffering to do what you must, because anything else would be inconceivable. It captures the joy of success, but also the painful loneliness. It evokes the frustration of failure and the soothing salve of friendship. In short, it inspires a reconsideration of the ways we typically characterize these experiences. And that’s the ultimate sign of a great work of art.