Following up on one of the greatest albums of all time is no easy feat. When Pink Floyd was tasked with doing just that, following up on Dark Side of the Moon, they were struggling. The record and its success had left the band jaded with the music industry. Eventually, the four-note riff of “Shine on You Crazy Diamond” became the catalyst for the album, as it reminded bassist Roger Waters of the somber story of their former lead singer, Syd Barrett. As the song finally came together, what none of the band expected was an unexpected appearance by Barrett in their studio.