Central banks are for the most part made up of legions of internists who stare at your X-rays and engage in sober consultations. At the end, they write diagnostic statements based on regularities and new facts – facts that can change your conditions in the longer run. We call regularities the “deep structure of the economy”. We call the new facts “shocks”.
The deep structure is formed by economic institutions, which take considerable time to develop. So central banks, not unlike doctors, take them largely as given. Shocks occasionally surprise economic agents, causing them to revise their medium-term outlook.