Money quote :
the real growth of the world economy sets long term limits on what kind of return is, on average, feasible. I cannot help feeling that the periodic asset bubbles that we have experienced in various forms reflect an unreasonable pressure in the financial sector to promise returns that in the aggregate cannot be achieved. These promises keep being made, however, and the assets bubbles keep being
encouraged, because the incentive structures that exist inside the financial sector are asymmetric. Managers reap great personal benefits from short term-profits but pay very little personal penalty when the bubble bursts. Moreover because asset bubble bursts affect the entire economy, there is always irresistible political pressure to socialize the losses when they become too threatening.