A folksinger (played by Oscar Isaac) navigates 1960s Greenwich Village in “ Inside Llewyn Davis.” (Long Strange Trip LLC)

“Inside Llewyn Davis” starts with a bang. Well, a wet, fleshy smack, really: Llewyn, a fictional 1960s folksinger having the worst week of his life, gets punched in the face.

“I think he deserves that punch,” says Oscar Isaac, a Golden Globe nominee for his turn as Llewyn in the Coen brothers’ new film, which opens locally this week. “But does he deserve everything else?”

“Everything else” includes having to crash on a series of couches, an unwanted pregnancy with his (married — to someone else) girlfriend, a failing career, the world’s worst road trip, and the cat he totes around Greenwich Village.

“I think this is a particularly hard week for Llewyn,” says Isaac, who reunites with “Drive’s” Carey Mulligan for the film. “I don’t think he’s necessarily always like this.”

Loosely inspired by real-life folk singer Dave Van Ronk, the Llewyn we see in the film is vaguely narcissistic, often hypocritical and just kind of a jerk — but still somehow likable. Essentially he’s that friend whose behavior you often have to justify to your other friends, even though you’re not quite sure why you like him.

“He’s an imperfect, fallible person,” Isaac says. “A lot of us, particularly in movies, have been conditioned that the lead character has to be heroic. I don’t understand that. In theater there’s a lot more leeway for characters to be all sorts of things.”

As Llewyn struggles through the ’60s folk scene, he watches as friends become successful doing music he considers inauthentic. That doesn’t stop him, though, from playing on a friend’s (Justin Timberlake) ridiculous novelty song to make a quick buck. Isaac says Llewyn is torn between his desire to connect authentically with the music he sings and, you know, needing a winter coat.

“I think he wants to fail just has much as he wants to succeed,” Isaac says. “I think he realizes this [authentic folk] music comes from a place of desperation. I don’t think he necessarily wants to put himself in a desperate situation, but I think he realizes that success might mean having to sell out a bit.

“If there’s any heroic deed [for Llewyn], at least he stays true to himself,” Isaac adds. “Even after getting punched in the face.”

That’s All Folk

The “Inside Llewyn Davis” soundtrack will be the rare album that’s a fixture in both your parents’ car and your sister’s dorm room. It combines traditional folk songs like “Fare Thee Well” and “Five Hundred Miles” with new tracks, such as standout earworm “Please Mr. Kennedy,” performed by Oscar Isaac, Justin Timberlake (who co-wrote the song) and Adam Driver (“Girls”), who sings backup vocals and periodically says “OUTER! SPACE!”