Two chords sound through the darkened concert hall, parting the silence like a hot knife. I raise my fingertips, commanding them to be still, and hoping that the judge can’t see their quivering. Softly, I play the next two chord progressions of Mendelssohn’s Rondo Capriccioso, carefully setting a framework for the piece whose impending weight bears down on my shoulders. I breathe deeply through my nose, pause at the top of a lingering chromatic scale, and dig my...