Following one's own passion in life is not always easy, and there is no certainty that things will go the way one hopes or expects. Suffice it to say, the drive to create art and the necessity for sacrifice oftentimes go hand in hand. Llewyn Davis (Oscar Isaac) knows this exceedingly well—and, in fact, has known it for quite some time. With no money for a place of his own, he hops around sleeping on the couches of his friends, acquaintances and older sister, Joy (Jeanine Serralles). Living in 1961 Greenwich Village, Llewyn once had a promising thing going as one-half of folk group duo Timlin & Davis until Timlin hurled himself off the Brooklyn Bridge. Now, he is trying to make a go at a solo career, picking up gigs wherever he can, but success in the music world is proving far more difficult than he could have imagined. It doesn't help that the girl he loves, Jean (Carey Mulligan), thinks he's a total loser, everything he touches turning to shit. She has just bitterly informed him she's pregnant, and is none too happy with not knowing whether the baby is Llewyn's or live-in boyfriend/music partner Jim's (Justin Timberlake).

Written and directed by brothers Ethan Coen and Joel Coen (2010's "True Grit"), "Inside Llewyn Davis" (named after the title character's unsuccessful solo album) is a poetic tribute to the universal drive to succeed and the search for happiness through one's chosen profession. For that matter, it is also about taking responsibility for one's actions, trying to better oneself by way of experience, and the frustrating hurdles and disappointments that are inevitably bound to rear their ugly heads sooner or later. A character piece both spirited and astutely told, the film's two constants are Oscar Isaac (2012's "Won't Back Down"), as Llewyn, and the soulfully melodic folk songs that become the soundtrack to his existence. Llewyn and his musician colleagues do not yet know it, but the peace-driven themes they sing about are on the verge of increasing in meaning and urgency with the obliteration of a generation's innocence—first with John F. Kennedy's assassination, and then with the start of the Vietnam War.

In an early scene, the struggling singer wakes up in the home of two of his few remaining friends, Columbia professor Mitch Gorfein (Ethan Phillips) and his wife, Lillian (Robin Bartlett), and accidentally locks himself and their cat out of the empty apartment. Even if he is a loser, as Jean labels him, he reveals to also be warm-hearted and compassionate, lugging the feline around the city with him until he can give the Gorfeins' pet back to them. When Llewyn makes the mistake of leaving Jean's window open and the cat jumps down the fire escape, it is yet another reminder that he cannot quit screwing up and letting people down. This cat, and a second one, will return throughout the film, a sort of whiskered emblem for Llewyn's drive to be a better, more reliable man. They are a clever throughline, these pussies, and are cause for a number of emotionally satisfying payoffs.

A talented real-life musician and a natural-born actor, Oscar Isaac more than lives up to the demanding requirements of his leading role. In every scene, Isaac sympathetically portrays a young man at a crossroads, one who has the chops of a musician but for whatever prickly reasons hasn't hit it big. In his line of work, you're usually either filthy rich or starving for that next paycheck, and Llewyn has not been able to escape this latter downtrodden category. "I'm so tired," he says to Jean late in the picture. "I thought it was just my eyes that were tired, but..." As he trails off, the viewer has followed him through all that he has been through—all of the would-be big breaks, the letdowns, the traveling, the lack of appreciation and validation—and understands what he means. Making memorable impressions with less screen time, Carey Mulligan (2013's "The Great Gatsby") plays Jean as a woman fed up with Llewyn's neediness and reluctant to admit that she still cares for him all the same, while John Goodman (2012's "Flight") and Garrett Hedlund (2010's "Tron: Legacy") are quirky loose cannons Roland Turner and Johnny Five, whom Llewyn hitches an unpredictable ride with to Chicago. Only effective when used in the right parts—and in moderation—Justin Timberlake (2013's "Runner Runner") is much more charismatic than usual as Jean's new boyfriend, Jim, hiring Llewyn to record a song ("Please, Mr. Kennedy") while being blissfully unaware of his romantic past with his girl.

If Llewyn is a character who most audience members will want to follow, it is the glorious folk music—largely original tunes co-produced by T-Bone Burnett, many songs divinely played from beginning to end—which gives the film its lifeblood. Isaac's performance of "Hang Me, Oh Hang Me" in the opening scene is sublime, and those that follow (among them, "Fare Thee Well," "Five Hundred Miles," and "The Death of Queen Jane") are all close to showstopping. "Inside Llewyn Davis" is an unforced, low-key drama, its story one that is more episodic than conventionally plotted. Not a lot is accomplished or resolved, and yet that is one of Ethan and Joel Coen's overriding messages. Rejoining the merchant marines—a possibility that he considers—is the worst decision he could make, even if it would mean having money and a roof over his head. Destined to forever suffer for his art and then be saved by it, Llewyn's journey, like himself, is a work in progress.