A pianist on stage realized she'd prepared the wrong piece. Then she pulled off a miracle.

A pianist on stage realized she'd prepared the wrong piece. Then she pulled off a miracle.

You know that nightmare where you show up to the final day of class and there's a huge test and you panic as you realize you've missed the whole semester and haven't studied at all? Or how about the one where you have to give a big presentation at work and you show up totally unprepared—no notes, no visuals, no speech—and you have to wing it?For musicians, the equivalent is showing up on stage to perform without preparation or rehearsal, which i…