" The risk models developed by private firms, whether hedge funds, rating agencies, or banks, are not reliable guides to the future. Even when these models are applied by government regulators, their application is flawed, because they look to past market history as received truth. But markets, we must emphasize, are imperfect; they are the agglomeration of myriad investors, most of whom usually act rationally - usually, as history has shown, but not always. Even perfectly logical investors will panic, as will theatergoers at the mere possibility of fire, so as not to be last to the exit; this threat of contagion renders financial markets inherently unstable. "
― Roger Lowenstein , When Genius Failed: The Rise and Fall of Long-Term Capital Management