Former Fed Chairman (1932-48) Marriner Eccles, who may well have been the most subtle economist of the 20th Century, from his memoir, Beckoning Frontiers (1966):
As mass production has to be accompanied by mass consumption, mass consumption, in turn, implies a distribution of wealth – not of existing wealth, but of wealth as it is currently produced – to provide men with buying power equal to the amount of goods and services offered by the nation's economic machinery. Instead of achieving that kind of distribution, a giant suction pump had by 1929-30 drawn into a few hands an increasing portion of currently produced wealth. This served them as capital accumulations.
But by taking purchasing power out of the hands of mass consumers, the savers denied to themselves the kind of effective demand for their products that would justify a reinvestment of their capital accumulations in new plants. In consequence, as in a poker game where the chips were concentrated in fewer and fewer hands, the other fellows could stay in the game only by borrowing. When their credit ran out, the game stopped.
I will again quote Mariner Eccles, from his 1933 testimony to Congress, in which he was himself quoting with approval an unidentified economist, probably William Trufant Foster. In his testimony he said:
"It is utterly impossible, as this country has demonstrated again and again, for the rich to save as much as they have been trying to save, and save anything that is worth saving. They can save idle factories and useless railroad coaches; they can save empty office buildings and closed banks; they can save paper evidences of foreign loans; but as a class they cannot save anything that is worth saving, above and beyond the amount that is made profitable by the increase of consumer buying.
It is for the interests of the well-to-do, to protect them from the results of their own folly – that we should take from them a sufficient amount of their surplus to enable consumers to consume and business to operate at a profit."