Last year, when Taylor Swift performed her song "New Year's Day" — the sweet, heartbreaking, final track on Reputation — on The Tonight Show, it ended up an indirect tribute to Jimmy Fallon's mother, Gloria, who had recently died. And when the song's co-writer, Jack Antonoff, appeared on the show on Thursday (March 8), he revealed a small bit of trivia that makes the song's emotional impact a little more surprising: "We wrote that song in a second," he said. "We didn't plan to write it."

"I think if you plan to write a ballad or something like that, you always get a little bit less than you hoped for," Antonoff continued, also revealing that his writing process usually involves just him alone or him with one other person. In this case, that person was Swift, though he notably worked with Lorde on Melodrama last year, too.

Antonoff was dressed like Paul Simon circa 1980 throughout this interview (which is kind of his general aesthetic anyway), where he also shouted out working with Harry Styles on "Alfie's Song (Not So Typical Love Song)."

"Well, you've met him," Antonoff said. "He's a cool kid." The entire chat is a lesson in not discarding ideas (like, say, humming a melody while making an English muffin) just because they may seem silly and frivolous in the moment. Check it out above, and then watch Antonoff and his band Bleachers perform a rousing, celebratory "Alfie's Song (Not So Typical Love Song)" — from the upcoming Love, Simon soundtrack — below.