It’s a new decade, but perhaps it’s wise to take one final look at what went wrong in the old one. The 2000 to 2009 period was one of only two decades since the 1920s in which the S&P 500 posted negative returns. The other, of course, the 1930s. Economist Robert Shiller says we only have ourselves to blame. Rather than save money in the bank, we came to rely on the stock market to build wealth, which led many to take on risky investments. The end-result: a rapid succession of boom and bust markets.