If you account correctly for stock buybacks made with borrowed money (even IBM does it) and option grants that obscure salary expenses, you get down to 4% profit real fast unless the economy zooms.

FORBES: Dow 10,000 -- in 2005

Modern portfolio theory the formula for diversification developed in the 1950s by economist Harry Markowitz, who later won the Nobel Prize for his breakthrough needs an urgent updating to account for the devastation that can be wrought by borrowed money, according to Zweig.

FORBES: Urgent: Investors Must Avoid Margin Ditch

Jacobs and Levy argue that modern portfolio theory the formula for diversification developed in the 1950s by economist Harry Markowitz, who later won the Nobel Prize for his breakthrough needs an urgent updating to account for the devastation that can be wrought by borrowed money.

WSJ: The Intelligent Investor: Borrowing Against Yourself