Stanley Fischer has been brave enough to admit the Fed simply does not know.
We simply do not know. The world is an uncertain place, and all monetary policymakers can really be sure of is that what will happen is often different from what we currently expect. That is why the Committee has indicated that its policy decisions will be data dependent. That is, we will adjust policy appropriately in light of economic and financial events to best foster conditions consistent with the attainment of our employment and inflation objectives.