You also should have enough to cover life's inevitable, unanticipated expenses, like a leaky roof or dead furnace not just in your primary home but also in all of your investment properties (which likely suffered abuse and neglect on their way to becoming bargains).

WSJ: Breaking the Home-Buying Habit -- WSJ House Talk

"This is an industry where if you get your costs out of line and business is not so good, you're dead, " says Sam Peltzman, a University of Chicago business school economics professor who studies labor and the airline industry.

FORBES: United We Fall

"This is an industry where if you get your costs out of line and business is not so good, you're dead, " says Sam Peltzman, an economics professor at the University of Chicago business school who studies labor and the airline industry.

FORBES: United We Fall