An old adage has it that you don't know what you've got 'til it's gone. But sometimes, you do know exactly what you have, when you have it. But you fail to appreciate it anyway, watching helplessly as it slips through your fingers, not entirely sure why you're not making an effort to hold on to it.

That difficult truth is at the heart of "Sleepwalk with Me," the endearing directorial debut of comedian Mike Birbiglia. This isn't your typical stand-up vehicle -- and thank goodness for that. Birbiglia brings us something less laugh-out-loud funny and more moving and meaningful.

That's not to say the comedian hasn't made a funny movie. But the humor isn't the point so much as what the things we find funny say about how we feel about other human beings.

"It all started when my girlfriend, Abby, and I decided to move in together," Matt (Birbiglia's alter ego) tells us. They've been dating for eight years, but no closer to marriage now than when they began seeing each other. "I never saw anyone married for 30 years and thought, 'I gotta get me some of that,' " Matt says, in the conversational tone his character uses throughout the film to make the audience a part of his not-very-successful life.

Abby (Lauren Ambrose) feels differently, of course. Matt first realizes this when he flips through the shows saved on their TiVo and finds multiple episodes of shows such as "Wedding Tales" and "Baby Tales."

Matt's a wannabe comedian who spends more time cleaning up the bathrooms at the bar than he does telling jokes on its stage. He should feel lucky to have kept the interest of someone as appealing as Abby. But, in fact, it's her almost-angelic nature that makes Matt want to rebel against the life everyone seems to have planned for him. "I think everyone thinks the best thing about my life is my girlfriend," he says.

That's a hard fact to face. For Matt, the anxieties such thoughts produce start manifesting themselves in his dreams, which he begins acting out while sort of sleepwalking, eventually leading to some injuries. But he's reluctant to get treated: He might have to admit he's not just nothing like the man he wants to be -- he's not really much of a man at all.

"Sleepwalk with Me" is based on Birbiglia's one-man, off-Broadway, semiautobiographical show. (He graduated from Georgetown in 2000, then worked the mop and took notes at DC Improv.) Humor often comes from exaggeration. Birbiglia's genius is in finding it in all-too-real situations -- and then going further and teaching us something about them while we laugh at his (and, hence, our own) foibles.