In 1960, [the great singer] Ella Fitzgerald was singing Mack the Knife to a crowd in Berlin. It was the first time she had sung the song and she started to forget the lyrics.
About to hit a dead end, her choice was clear: Do I stop and apologize, admit that I have no idea where I’m headed, or do I keep on going and try to make the best of things?
Ella kept going, making up new words as she went along. They rhymed and fit the music, and her performance was a tour de force.
Fortunately, the show was being recorded and a record was released later that year . . .
Ella’s recording of Mack the Knife won her a Grammy Award for Best Female Vocal Performance.
-- from If You Can Talk, You Can Write by Joel Saltzman