Why We Buy

How simple promotional tactics trick us into buying more at the store.

By PT Staff, published on March 01, 1999 - last reviewed on January 08, 2009

Brian Wansink, of the University of Illinois, is founder of the Food and Brand Labs, which employ test kitchens, grocery stores, and families to study why we choose to buy certain foods and household products over others. He spoke with PT about promotional tactics that can trick us into buying more at the store.

Why study consumer behavior?

We make between 30 and 40 food-related decisions a day. You might think, Does it really matter if I buy three cans at the store instead of one? Or an extra cup of coffee? But over time, these decisions have a big impact on the money you spend—and on your nutrition.

What makes us buy more at the store?

Our biggest problem? Store signs with numbers. When a display reads "Limit 12 per customer" or suggests "Buy 12 for your freezer!," consumers will buy up to twice as much as they would without a sign. Another problem is confusion. When consumers see an item promoted as "4 for $2" instead of "50 cents each," they're not sure whether you must buy four to get the deal. So they do.

Why do we fall for these traps?

I think most shoppers aren't dumb. They're smart not to allocate huge amounts of attention to making sure they save $4; they'd be paralyzed every time they went to the store. Is it worth a lot of effort? No. But it's worth a little bit.

How can we become more vigilant?

There are two types of consumers. The high-involvement consumer makes lists of what they want each time they visit the store. For them, penciling in the exact number of what they want to buy can keep them from purchasing more. There are also the impulse shopper who buy what he wants when he wants it. He should try to remember that every time he sees a number in a store sign, he's likely to buy at least one more item than intended.