Movements in certain types of input costs, particularly changes in the price of imported goods, also can cause core inflation to deviate noticeably from its trend, sometimes by a marked amount from year to year. 17 Finally, a nontrivial fraction of the quarter-to-quarter, and even the year-to-year, variability of inflation is attributable to idiosyncratic and often unpredictable shocks.
If your predictions are based on sophisticated models that have never heard of traffic lights and have been estimated over complex roundabouts and multi-lane intersections, you just don’t get that simple fact. It is even technically difficult to devise ways to put red lights into standard models by way of ad-hoc dummies and add-ons.