In 1481 Leonardo da Vinci was commissioned to paint an altarpiece for the chapel of a nearby monastery. He devoted an inordinate amount of time and energy to the depiction, compiling countless preparatory sketches and carefully attending to each intricate detail. The result was revolutionary: one of the most dramatic and innovative renderings of the Renaissance, before which succeeding generations of artists would later stand awestruck in absolute wonder. Mysteriously, though, just seven months into the portrayal, Leonardo abruptly set his brushes aside and never returned to resume his work. To this day, the Adoration of the Magi remains an unfinished masterpiece.

In early October 1822, Franz Schubert began the preliminary piano outlines for his Symphony No. 8 in B Minor. Within a few wee…