Such accounts may be exaggerations, but they should warn us that yearly progress is never assured. Instead, history offers plenty of examples of life becoming far worse than it had been centuries earlier. The biographer Plutarch, writing 500 years after the glories of classical Greece, lamented that in his time weeds grew amid the empty colonnades of the once-impressive Greek city-states. In America, most would prefer to live in the Detroit of 1941 than the Detroit of 2011. The quality of today’s air travel has regressed to the climate of yesterday’s bus service.