Pushing On A String

Pushing on a string is a figure of speech for influence that is more effective in moving things in one direction than another – you can pull, but not push.

If something is connected to you by a string, you can move it toward you by pulling on the string, but you can't move it away from you by pushing on the string. It is often used in the context of economic policy, specifically the view that "Monetary policy asymmetric; it being easier to stop an expansion than to end a severe contraction."