Comedy is fun -- isn't it?

Conflict emerges in a group of improvisational comics in Don't Think Twice.

Don't Think Twice introduces us to a group of improvisational comedians trying to make it in the highly competitive world of New York-based show business.

Comedy may aim for laughs, but as a business, it's not all yucks. That means we shouldn't be surprised that Don't Think Twice contains some of the year's more painful moments as it skillfully assess success, failure and the hairline difference between the two.

Writer/director Mike Birbiglia, who also appears in the movie, tells the story of The Commune, men and women comics who share a New York City apartment. They're one big happy family -- until, of course, they're not.

Group solidarity runs into trouble when The Commune faces the loss of its performance space. On top of that, troupe members Jack (Keegan-Michael Key) and his girlfriend Samantha (Gillian Jacobs) have been invited to audition for Weekend Live, a big-time comedy show that looks a lot like Saturday Night Live.

Jack's sudden rise to recognition, throws the rest of the group into turmoil. He promises to help the others get auditions or writing jobs, but we know that it's probably an empty pledge. Nothing like a splash of success to undermine a one-for-all spirit.

And for every upward arc, a corresponding downside lurks. Bill (Chris Gerhard), for example, has been working at comedy for a while, and isn't convinced that he'll ever have a breakthrough moment. He's also dealing with a disapproving father, who has been diagnosed with a serious illness.

Look, one of the saddest things in life involves watching people who keep striving long after their expiration date has passed. And some of these characters are right on the cusp of such failure.

To the extent that The Commune has a leader, the job falls to Birbiglia's Miles. Miles once auditioned for Weekend Live, but didn't make the cut. In addition to his work with The Commune, Miles teaches improv. He tries to convince himself that his approach involves a purity that he couldn't maintain if he actually were to get a shot at the world's best-known comedy TV show.

One of the troupe's members winds up delivering a piercing rebuke to Miles, who eventually reunites with an old high school classmate (Maggie Kemper) with whom he'd like to begin a relationship.

It's easy to be dismissive about the characters in Don't Think Twice. Who in his or her right mind really believes he or she can make it in the cut-throat world of comedy? And don't we have bigger problems to worry about, anyway?

We do, but at its best, Don't Think Twice makes us feel for those who must abandon long-held dreams, a phenomenon not unknown outside the world of comedy. It's difficult for everyone to reach the point at which youthful hopes begin to fade.

So credit a canny Birbiglia -- a comic -- with knowing the milieu he's depicting and for doing it in ways that never become such an in-group exercise that we lose touch with the characters.

Don't Think Twice may not be a momentous movie, but it's perceptive and honest enough to demand what the best comedies require: Occasionally, it wants to be taken seriously.