Greenspan's Role

One other key player that Siegel criticized for not heading off the collapse of the mortgage-backed securities is former Federal Reserve chairman Alan Greenspan, who oversaw the government's central bank until 2006. Greenspan was so influential while he oversaw the Fed that he could have easily blown the whistle on the over-accumulation of mortgage-backed assets by the U.S.-based financial giants. He, however, failed to discover that firms were taking such large, risky individual stakes without protecting themselves against a housing market collapse. "[Greenspan was] the greatest central banker in history -- he had access to every piece of data," Siegel said. "He could have looked at the balance sheets of Morgan Stanley or Citigroup and said, 'Oh my God -- they didn't neutralize their risk.'"

Another reason why federal officials and economists failed to detect the perilous economic risks of the 2000s, Siegel said, is the so-called "Great Moderation." This term refers to the fact that since the 1980s, the volatility of the business cycle has declined, thanks to more aggressive fiscal policy and the rise of a service-based economy, among other factors. Siegel noted that a similar flattening of the economic cycles had occurred during the 1920s after the 1913 establishment of the Federal Reserve Bank, a factor that caused stock investors to ignore risks, which eventually led to the stock market crash of 1929 and the Great Depression.

"People asked, 'Are we ever going to have a big recession again?'" Siegel said of today's policy makers. "Everybody thought we were in a new stage and risk premiums didn't need to be so high." But those risks hit home last year. While it would have been difficult for federal regulators to save Lehman Brothers -- which had invested billions of dollars in assets related to subprime mortgages -- even if they had acted six months sooner, the fall of the 158-year-old financial house had a disastrous impact on the wider financial market. Lehman Brothers was connected to 950,000 or so transactions. As a result, bankers became gun-shy about making any type of loan, even to companies with a flawless credit history.