It's happy hour at Hanaro in Bethesda, Md., and I'm with my wife. We're there about an hour, gobbling plates of half-price tuna rolls and washing them down with $3.50 Blue Moons. Have to hurry, happy hour ends soon. My wife slows down and cautions me to do the same. I don't listen. Keep 'em coming, right up to 7 o'clock. Then I get the bill: $75. Yikes, how did that happen? I thought this stuff was half price! Call this stupid male tricks — or behavioral economics.

Behavioral economics tries to figure out why people consistently make irrational financial decisions — like paying $75 to jam 15 orders of sushi down your throat in an hour. The bar happy hour embodies two classic ploys that cause irrational choices: scarcity, get it now before it's gone; and the idea of getting something for nothing, buy two pairs, get the third free.

"If you think something is going away, it can lead to excessive and desperate consumption," says George Loewenstein, a professor of economics and psychology at Carnegie Mellon University in Pittsburgh.