Back in September 2013, McDonald’s began a campaign for their Premium Roast Coffee. Started in California, the campaign (perhaps due to its success) has grown countrywide. Buy any size cup of coffee, at any time of the day, and it’s only $1. Small, medium or large – your choice – only a buck. It sounds great, until you understand the behavioral modification occurring. Let me walk you through it:

1. Regardless of the size coffee you bought in the past, with all the prices the same you will positively buy the largest size. If you buy anything but a large cup you feel that you are getting jipped. If you buy the large, you feel you got the best deal.

2. Here’s the trick: Mickey D’s wants you to buy the large cup. And they want you to buy it repeatedly. They want you to buy it enough times so that you re-define yourself as a large cup of coffee drinker.

3. When the prices return to their normal tiered structure, you are highly likely to continue to buy the large size (even if you drank small before), because you have now defined yourself as a large.

McDonald’s is employing a behavioral modification technique of self-assigned labels. We act consistently with how we define ourselves. And if we see ourselves as a large cup of coffee drinker, regardless of minor price changes, we will keep buying the large cup of coffee.

We all label ourselves in different ways. We drive a certain type of car, and then stick with the brand (or at least the brand image). There are big pickup truck folks and there are mini-electric car folks and the two shall never meet. We call ourselves athletic or lazy, or horrible at math or great a history, and then act accordingly.

There are folks who say “I am a small cup of coffee customer,” and others that say “supersize me.” McDonald’s makes more money from the supersize folks. But how do you get people to change their self-assigned label? You make the price the same for all sizes. Then you have them buy the large cup repeatedly. Until one day, those former “small cup” people starting seeing themselves as “supersizers”. Their definition of themselves has changed, and with it their buying behavior.