“Shine On You Crazy Diamond” was written about Syd Barrett (his nickname SYD is directly referenced in the title’s initials), one of the original band members. Barrett departed the band after the release of their first record, Piper at the Gates of Dawn, due to his fragile mental state (made worse by his casual usage of LSD), and replaced by David Gilmour.
Barrett always remained a source of inspiration. In fact, after many years of no contact with any of the band members, Barrett randomly walked into the studio with a shaved head during the recording sessions of this song. Roger Waters, his childhood friend, didn’t even recognize him at first. After about forty-five minutes, he broke down in tears in distress when he realised this stranger was his old friend.