Almost 10 years ago, Matt Foster wrote the song that would become one of the biggest hits of the decade.

One day in January 2010, Foster spent eight hours writing and singing a synth-filled single with a cheery beat that belied its somber lyrics. By the next year, Foster the People’s Pumped Up Kicks was on the Billboard Hot 100, and listeners wanted to know why Foster had written about what appeared to be a school shooting.