Imagine it is late 2024. Inflation in the rich world has fallen from its peak but stayed stubbornly high. At around 4%, it is well above the level at which most central banks are comfortable. Governments, weighed down by vast debts, must use precious revenues to pay interest on the debt, which itself is growing because of high interest rates. The energy transition and rising state spending owing to ageing populations add to the fiscal largesse. Raising taxes is politically fraught, so more money is printed. Inflation stays high and governments’ credibility worsens. Central bankers are scratching their heads, wondering how their powerful weapon—the interest rate—has failed so thoroughly.