a simple rule of that sort will, by necessity, leave out many factors that appropriately influence monetary policy, such as financial developments, temporary divergences in relationships between different measures of economic activity or inflation, and the like. A simple rule can provide the starting point for the decisions made by the FOMC, but in reaching their interest rate decision, members of the Committee will always have to use their judgment to identify the special circumstances confronting the economy, and how to react to them.
Pointer from Mark Thoma.
The shorter version- “How can we pretend to know what we are doing if you don’t let us?”