Hence, although a given propulsive force always has the same, predictable effect on a ballistic missile, a given policy action--say, a 25-basis-point cut in the federal funds rate--can have very different effects on the economy, depending (for example) on what the private sector infers from that action about likely future policy actions, about the information that may have induced the policymaker to act, about the policymaker's objectives in taking the action, and so on.
Thus, taking the "right" policy action--in this case, changing the federal funds rate by the right amount at the right time--is a necessary but not sufficient condition for getting the desired economic response. Most inflation-targeting central banks have found that effective communication policies are a useful way, in effect, to make the private sector a partner in the policymaking process.