I don't know, did Keynes ever understood how capitalism works? Capitalism is competition. If your employees work less, your competitor's employees will work full time and overtime, getting their product to market faster and reaping all the rewards. It works with entire countries as competitive agents (see China). "Winner takes it all" operation mode of modern markets amplifies the magnitude of the problem.<p>Another issue is management overhead. Managing 10 people working full-time is easier (perhaps exponentially) than managing 40 people working 1/4 time. Easier means cheaper, which means that you are better positioned in the competition. This is why every rational company will hire 10 people full-time and leave the other 30 unemployed, instead of hiring all 40 for quarter of the time.<p>I see no solution to this problem in peacetime (Keynes' own solution famously didn't work). In wartime, of course, there are nearly no unemployed.