Heroes of the Zeroes is Nick Rogers’ daily, alphabetical look back at the 365 best films of 2000 to 2009.

Once a musician, always a musician — as far as spark, if not skill, is concerned. That sincere belief in music’s lasting creative and cathartic power propelled Once — a sweet, simple, stunning 2007 film about a male Irish guitarist, a female Czech pianist and their music.

Whether Once connected as the greatest unconventional musical since Dancer in the Dark depended largely, as did Dancer, on what viewers thought of the tunes themselves. Smart money says most audiences for Once ponied up for the soundtrack.

The haunted eyes of Glen Hansard, the optimistic smile of Marketa Irglova and their complementary musical talents lead to an uninterrupted take in which they piece together a ballad called “Falling Slowly.”

Verse by verse, the song reveals two people sharing the same emotional language and, even if neither yet knows it, a dream of composition. Deservedly, “Falling Slowly” bowled over Oscar voters for Best Original Song.

Once would seem to point down a path to romantic harmony, but the duo’s courtship grows complicated by how emotional torment and musical creativity go hand in hand. Eventually, the film becomes a bittersweet ode to how plans of wild escapes and different lives concocted in feverish late-night reverie can melt when the morning light exposes them as pipe dreams.

Like all great pop songs, you can’t wait to hear how it ends, and few endings felt as complete as that in Once — joyfully attuned to the tumultuous nature of making music, and a love, that will endure.