"So let’s look at the NBER business cycle data. What we see is that some of those prewar slumps were really, really long: the Panic of 1873 was followed by a recession that lasted 5 1/2 years.
And Keynes explained why: in the absence of an effective monetary or fiscal policy, a recession would have to go on until
the shortage of capital through use, decay and obsolescence causes a sufficiently obvious scarcity to increase the marginal efficiency
So this could go on for a long, long, long, long time."