The video has been sent to me as a comment by Kevin Reider which is sincerely appreciated. I will mention that this blog does not publish comments but I do read them all.
I will only briefly comment myself, that the video uses Keynes’s definition which is “supply creates its own demand”, which is similar to the classical “demand is constituted by supply”. But the real point of it all is this: “there is no such thing as deficiency of demand”, or in the words of the classics, “there is no such thing as a general glut”. Exchange is relatively easy to understand. Why public spending in recession will not bring about recovery is almost impossible, but that is the challenge.