When it was released in 1978, the Rolling Stones song “Beast of Burden” was an instant hit, remaining in the Billboard Top 10 for 13 weeks. Keith Richards says he finds that fact amusing, considering most people don’t know who the song was written about. Even Richards isn’t 100 percent sure. The guitarist tells Harper’s Bazaar the track was inspired by singer Marianne Faithfull or actor-model Anita Pallenberg. Faithfull, who scored a hit with the Stones’ “As Tears Go By,” was once in a relationship with Mick Jagger — until she cheated on him with Richards. Pallenburg is the mother of three of Richards’ children. “Some of the theories surrounding it are very intriguing, but they’re about as divorced from reality as can be,” Richards says of the classic track. “I find it quite amusing that there are people in the world who spend a lot of their time trying to decode something that is, at the end of the day, completely undecodable. I mean, even I’ve forgotten the code!”