Mike Birbiglia's Don't Think Twice stands as the best, most revealing film about comedy people and one of the best about artistic collaboration. It's a boisterous and sensitive work of many facets: tender group portraiture, bang-on media satire, evenhanded inquiry into the ethics of selling out. Above all that it's an introductory course in improv stage comedy, a work of advocacy for the scene it surveys and -- through its warm fascination with improv's trust-your-group ethos -- something like a cult indoctrination. Birbiglia runs down the key rules of improv (say yes to your scene partners' ideas, put the group before yourself) and then shows us how they shape the performances of Commune, a troupe at a struggling UCB-like theater in Manhattan.
Of course, those rules, derived from the teaching of Del Close, can apply to life, too, and Birbiglia's film cannily shows us how the Commune tries -- and sometimes fails -- to live up to those ideals.
The film's heart, though, is shared by Sam (Gillian Jacobs) and Jack (Keegan-Michael Key), who play lovers within the group. Cocksure Jack and uncertain Sam get invited to audition for a venerable SNL-like TV show, and Birbiglia's plot from there smartly charts the fallout: Is Jack wrong to violate the group's egalitarian ethos to win his own shot at stardom? Are the other Commune members wrong to hold a grudge?
Sam, meanwhile, faces down anxiety of the sort that's usually played for sad laughs in indie comedies. In the end, when Sam's started to piece herself together, and to make peace with being broke but creative, Jacobs is giving the richest, grittiest performance of her career, laying bare the character's heart through her stage work.