premise: "I'm Not the One" is a song by the American rock band The Cars, from their fourth album, "Shake It Up". It features Ric Ocasek on lead vocals, Benjamin Orr singing the 'You Know Why' phrase, with the whole group repeating "going round and round" as backing vocals throughout the song.
hypothesis: Elliot easton sang backup vocals
reason: Elliot Easton is the lead guitarist for The Cars, and would be available to sing backup vocals. The context implies that the rest of the group besides Ric Ocasek and Benjamin Orr participated in backup vocals, but it cannot be explicitly determined if Elliot Easton did or did not sing backup vocals