Imagine you are in a concert hall. A virtuoso pianist is seated at a gorgeously polished Steinway grand. The concerto begins. The music is beautiful, breath-taking. Everything is perfect.
But then, a few minutes into the piece, the pianist misses a key. The first time it happens, it’s almost unnoticeable – and extra D, perhaps, in a chord that doesn’t need that note. Embedded in so many perfectly played notes, hidden among the otherwise flawless chord in an otherwise perfect melody, it’s nothing to worry about. But then, a few minutes later, it happens again. And then, with increasing frequency, again and again and again.