“Don’t Think Twice”

Rated R (1:32)

***

Opens today at Kahala 8

Like its improv troupe protagonists, “Don’t Think Twice” is a film that is at its best on stage.

Writer-director Mike Birbiglia clearly loves the purity of improvisational comedy, and he makes it the mission of his film to explain that love to the masses. There are many moments that don’t ring true from a narrative standpoint, but they don’t detract from the message: Improv is beautiful, difficult and fleeting, and its practitioners suffer for their art.

The momentum for “Don’t Think Twice” is provided by its wonderful comedy cast, including Keegan-Michael Key and Gillian Jacobs as Jack and Samantha, a New York couple who are opposite on the ambition spectrum. Samantha is true to the comedy, but Jack is more selfish. Knowing there’s a producer for “Weekend Live” in the audience for one of their small club shows, Jack showboats — a cardinal sin in improv. The fallout threatens to tear the group apart.

The twists and turns in their personal lives often feel inauthentic — like script devices to propel the action. The film is filled with conveniently timed tragedies, illogical behavior in service of the plot and heavily telegraphed solutions.

But the characters themselves remain genuine. Like Tom Hanks in “Punchline,” Key is a beloved actor who explores a darker version of himself, allowing for some interesting nuances. He’s willing to help his friends, up until the moment that it hurts his own path to fame.

Each of the key actors — Birbiglia, Key, Jacobs, Kate Micucci, Chris Gethard and Tami Sagher — have real-life experiences that reflect their characters. The result seems to be an asset during the improv scenes, which charge the movie with the authenticity that it lacks off the stage.

Birbiglia’s writing also captures the gallows humor, insecurities, paranoia and bonding between struggling comics. The group is volatile and merciless at times, but they also forgive quickly and have incredible loyalty. This, if you’ve met a lot of comics, is an accurate description.