Federal Reserve policy makers tend to believe temporary shocks account for the persistent undershooting of the inflation target. But there’s a more disturbing possibility: Central bankers might just be using a broken model of inflation. Given that risk, they should pay attention to actual inflation and lean toward passing on a December rate hike. Nonetheless, they are prepared to move forward. The dismissal of actual data given these very real concerns about the forecasting accuracy of the Fed’s models could place us in a more dangerous stage of the business cycle.