There are no obvious limits to what central banks can do. The suspicion that they might really run out of tools and ideas is understandable, but it is backward-looking and has proved groundless more than once already. My considered response is that we now have enough information to reject the conclusion that the recent monetary policy initiatives did not work.
There is an apparently technical but actually crucial point that I would like to make before getting to the crux of the matter. To assess a policy intervention (monetary or otherwise), one  1  From this perspective the Great Depression is considered an outlier, a unique historical event with limited general lessons on the cost of deflation.