The old saying, “You only hurt the ones you love,” took on new meaning in a recent report from Duke University. In it, the authors analyzed an interesting phenomenon: when one person in a relationship is frustrated with the other, he or she will often deliberately buy brands the other doesn’t like as a way of expressing his or her anger. The study also found that this still occurred even when the frustrated party personally disliked the brand they were choosing for spite and, here’s the real kicker, in many cases, the other party never even knows it happened.

In other words, people are thinking (feeling, really), “I’m drinking this yucky Diet Pepsi because I know you like Diet Coke.” (Or, ya know, vice versa.) In a report on the Duke study, NPR’s social science correspondent Shankar Vedantam said, “The people who are likely to behave this way are often people who feel powerless in their relationship. So, you feel you’re not being heard. You express your frustration through this kind of low-key oppositional behavior.”

Apparently some people use brands as a weapon, but what’s really intriguing here is how much this kind of “oppositional” brand choice reflects the core of what makes brands tick. In that light, none of this should be that surprising.

Core brand principle #1. People buy brands that make them feel better about themselves. There is a hardwired connection between self-esteem and brand choice. People buy a premium brand of food or beverage for a party because they want to feel like a good host or hostess. They donate to a certain charity because they want to feel altruistic. It may be a bit twisted, but people will also buy a brand they don’t like as a way of feeling like they are winning the battle with a person they are angry with.

Core brand principle #2. Brand connections are based on emotions. This goes beyond the core of self-esteem to broader issues. Loyalty to a brand can reflect a sense of belonging, as in “I’m part of a team or tribe that believes in this brand.” It could be a sports team or a brand of clothing, but who hasn’t met someone and learned they like a brand that you do and instantly felt a bit of a connection with that person as a result? “Oh, you like brand X? I love brand X!”

Core brand principle #3. People define themselves and others by the brands they buy. So, unless we are angry with someone, our brand choices will usually reflect how we feel about ourselves and, to a certain extent, our self-image. This can certainly be complicated. A person who thinks of himself as economical for buying a car brand with a reputation as long-lasting, may also feel he deserves a certain luxury by purchasing an expensive brand of coffee every day. But, clearly, we also judge other people by their brand choices and react to them. A person might admire a neighbor who drives a Mercedes and wish they had one, too. Or, they might criticize that neighbor for being extravagant and making poor choices with their money.

Either way, using a brand choice as a demonstration of emotion, whether positive or negative, is really what brands are all about. Have I ever bought a brand to be “oppositional?” You bet. Haven’t you?