In one of the most delightful sequences in director John Carney's Once follow-up, Begin Again, the characters played by Mark Ruffalo and Keira Knightley traipse around New York using a headphone splitter to listen to music together. One of the tunes that plays is Dooley Wilson's "As Time Goes By," the song best associated, of course, with Casablanca

"That’s the only song in the film that has a message behind or a plan behind a little bit," Carney said in an interview with The Wire on Thursday. "It’s such a great song. I think that kids don’t know that song and younger people don’t quite know that song. I think it’s great to try and sort of keep those things alive a little bit. And I suppose things are moving so quickly nowadays that it’s nice to put things in films for younger people that they’ll go, 'What’s that from?' Because we all know that it’s from Casablanca."

There's perhaps another subtle, unintentional reason that the song makes sense in the film, which is also filled with original music from Gregg Alexander. The movie tells the story of Gretta (Knightley), a young songwriter who is ready to say goodbye to New York after her boyfriend (Adam Levine) hits it big in the music industry and cheats on her. She is discovered playing at an open mic night by Dan (Ruffalo), a recently fired record executive, and they decide to make an album together, recording it in outdoor locations around the city. The movie does feel like a version of Carney's Once in that it has a loose storyline and mostly revolves around the making of music. It just happens to take place in a different city and has celebrities in the cast. 

Oh, and the two leads—spoiler alert for both movies—don't end up together, at least in a romantic way, at the end. "I guess I like those endings a little bit because I don’t really believe in the happy ending, walking off hand in hand through the flowers, in life," he told The Wire. "It just is not how life has been for me. It has always been complex." Carney explained that there's something "voyeuristic" in watching other couples fall in love. "And then the presumption is that you go back to your own drab life and Jennifer Aniston isn’t there," he said. "Or whoever the romantic lead is, isn’t there. I think you should be inspired when you go see a film to sort of address things in your life a little bit. Or to reflect on the film that you’ve seen and see things aren’t perfect. It seems as well I don’t know that any classic love story has ended with a happy ending."

So we asked him if maybe that's another reason why he chose "As Time Goes By." After all, Ingrid Bergman's Ilsa does get on the plane with Victor Laszlo and doesn't end up with her great love, Humphrey Bogart's Rick. "Oh interesting. Maybe inadvertently," he said. "Maybe there’s a Casablanca reference in it that I didn’t plan."