Pianist’s nightmare
Portuguese pianist Maria Joao Pires was expecting to play a Mozart piano concerto live with the orchestra -- just not the one they started playing. When she objected, while the orchestra played on, the conductor, Riccardo Chailly, replied, "But you play this one so well!"
She then, amazingly, switched over to the unexpected concerto. She has an astonishing memory!
See an excerpt here (3:38):
https://www.youtube.com/watch?v=rVO26URqC24