THE world expects a lot of its central bankers. Politicians demand that they control inflation, keep the economy growing and the financial sector stable. At times, central banks seem to do all the work: it was Mario Draghi of the European Central Bank, not the leaders of Germany and France, who stopped the sell-off in euro-zone bond markets in 2012, for example. Sometimes politicians seem to be sabotaging the central bankers, tightening fiscal policy when the banks are easing to help the economy.