“If you have never understood why an old saying calls opera ‘the most expensive human endeavor, with the possible exception of war,’ a day at the Metropolitan Opera explains it. The divas, maestro, managers and orchestra are just part of the equation. So much else goes into the productions, made more complicated by the Met’s tradition of staging operas in repertory. The Met is often a 24-hour operation. Make that a 24/6 operation, and occasionally 24/7.”