Decades ago, when I was a student at one of the London conservatoires, I discovered just how difficult conducting really is. With the cockiness of youth I reckoned it was something I could add to my portfolio of skills without too much trouble. I signed up for a course, and soon found myself in front of a student orchestra, with a Brahms symphony on the music stand. I gave what I thought was a clear upbeat into the piece, and almost immediately things started to fall apart. The winds raced ahead of the violins, the basses lumbered in their wake. The horns missed an entry, probably because they were laughing. Meanwhile I flailed on. Brahms’s carefully contrived texture disintegrated like a ghastly slow-motion car crash.