Why do our headaches persist after taking a one-cent aspirin but disappear when we take a 50-cent aspirin?

Why does recalling the Ten Commandments reduce our tendency to lie, even when we couldn't possibly be caught?

Why do we splurge on a lavish meal but cut coupons to save twenty-five cents on a can of soup?

Why do we go back for second helpings at the unlimited buffet, even when our stomachs are already full?

And how did we ever start spending $4.15 on a cup of coffee when, just a few years ago, we used to pay less than a dollar?

When it comes to making decisions in our lives, we think we're in control. We think we're making smart, rational choices. But are we?

In a series of illuminating, often surprising experiments, MIT behavioral economist Dan Ariely refutes the common assumption that we behave in fundamentally rational ways. Blending everyday experience with groundbreaking research, Ariely explains how expectations, emotions, social norms, and other invisible, seemingly illogical forces skew our reasoning abilities.

Not only do we make astonishingly simple mistakes every day, but we make the same "types" of mistakes, Ariely discovers. We consistently overpay, underestimate, and procrastinate. We fail to understand the profound effects of our emotions on what we want, and we overvalue what we already own. Yet these misguided behaviors are neither random nor senseless. They're systematic and predictable--making us "predictably" irrational.

From drinking coffee to losing weight, from buying a car to choosing a romantic partner, Ariely explains how to break through these systematic patterns of thought to make better decisions. "Predictably Irrational" will change the way we interact with the world--one small decision at a time.

Dan Ariely is the James B. Duke Professor of Behavioral Economics at Duke University. He also holds an appointment at the MIT Media Lab where he is the head of the eRationality research group. He was formerly the Alfred P. Sloan Professor of Behavioral Economics at MIT Sloan School of Management.

Dan Ariely grew up in Israel after birth in New York. He served in the Israeli army and when 18 suffered third-degree burns over 70 percent of his body from an accidental magnesium flare explosion during training.

Ariely recovered and went on to graduate from Tel Aviv University and received a Ph.D. and M.A. in cognitive psychology from the University of North Carolina at Chapel Hill, and a Ph.D. in business from Duke University. His research focuses on discovering and measuring how people make decisions. He models the human decision making process and in particular the irrational decisions that we all make every day.

Ariely is the author of the book, Predictably Irrational: The Hidden Forces That Shape Our Decisions, which was published on February 19, 2008 by HarperCollins. When asked whether reading Predictably Irrational and understanding one's irrational behaviors could make a person's life worse (such as by defeating the benefits of a placebo), Ariely responded that there could be a short term cost, but that there would also likely be longterm benefits, and that reading his book would not make a person worse off.