Look at Hyrum Minsky, an old Keynesian economist who never really bought into the efficient market hypothesis. He tried to describe why bubbles occur. His explanation was that they grew out of too much stability. As financial markets stabilize and grow, they can go from the relatively conservative principles that got them there to a willingness to take on more risk. Values are rising, and financial institutions don’t want to be left behind while other institutions are making loans to non-traditional borrowers. As long as values keep increasing the economy keeps improving, many of these borrowers won’t have much issues repaying the loans. But at a certain point, values don’t keep pace, and some of the non-traditional borrowers are getting loans that they can’t even afford the interest on. They are the first loans to fail. That sets off a domino effect in which values fall, the next level of non-traditional loans fail, and then values fall again. Sometimes, too much stability can lead to instability.