. >> reporter: economist david kotz: >> if the economy's going to expand, while profits are going upy rapidly and wages are stagnating or falling which has been the rule since 1980, then who's going to buy increased output of the economy? it's possible only if households borrow to maintain their living standard. and that's why we've seen the huge growth in household debt in the economy. millions of families unable to pay their bills from their declining income were forced to borrow against their home to, to keep the electric power on. >> reporter: professor david moss of the harvard business school agrees. >> as the crisis was in full swing in late 2008, november- december 2008, i started to put together a graph, a simple chart on bank failures in the 19th and 20th century up to the present. and a really very striking pattern emerged. >> reporter: striking, says moss, was the resemblance between his bank failure chart and a graph of u.s. income inequality over the last century. >> sure enough, the match with bank failures was remarkably strong. inequality peaked just before the finan