While uncertainty about the natural rate provides a useful illustration of one type of uncertainty policymakers face, it isn't the only type the Fed faces. The Fed also cannot be sure of exactly how its actions will affect the economy. Imagine you are driving a car. Very cautiously, according to Brainard. When a policy action's impact on output and inflation is hard to predict, it becomes optimal to respond cautiously to new developments.
Uncertainty can lead to caution.
Recent research has suggested the answer to this question is yes. Suppose you are driving along a narrow ridge, buffeted by gusting winds, and the linkage between movements in your steering wheel and the car's response is hard to predict. A strong blast of wind could push you over the edge. You don't know where the next gust will come from. Better to risk over-steering than to find yourself over the edge.