There's no automatic mechanism in a market system that reconciles the desire to save and the desire to invest. And therefore, the government has to sort of do something or the Federal Reserve, the Fed, or the Central Bank, or whatever, it has to intervene. It has to create enough investment for the economy not to suffer from a fall in aggregate demand. So, if you don't have a balance within the market system itself, then you need an external balance and that's what I think Keynes believed.