What allowed some people to see the financial crash coming while so many others missed its gathering force? I put that question recently to Nouriel Roubini, who has come to be known as Dr. Doom" because of his insistent warnings starting in 2006 that we were heading into a global firestorm. Roubini gave two kinds of answers. The first involves standard number-crunching of the sort that economists routinely do -- and that Roubini just did better and sooner. It's his second answer that's more interesting, because it goes to the heart of what we should take away from this crisis: Roubini decided to discard the assumption of market rationality that underlies most economics and to embrace the psychological insights of what's known as "behavioral economics." Everyone else had those same numbers. Why did Roubini act? The answer is that he decided to trust his gut, which told him there was trouble ahead, rather than Wall Street's "wisdom of the crowd," which -- as reflected in stock prices -- said everything was rosy. He concluded that the markets were not pricing in the degree of risk that was actually present in housing. "The rational man theory of economics has not worked," Roubini said last month at a session of the World Economic Forum at Davos. That's why he and other prominent economists are paying more attention to behavioral economics, which starts from the premise that economic decisions, like other aspects of human behavior, are influenced by irrational psychological factors.