PROGRAMMING NOTE: Watch CNN Original Series “Live Aid: When Rock ’n’ Roll Took On the World,” celebrating the definitive story of how two rockstars inspired the largest global music events in history.

(CNN) — Paul McCartney hadn’t taken the stage in over five years when he sat down at his piano to sing “Let It Be” for Live Aid on July 13, 1985, in a performance that was almost totally derailed by a ...