Turns out, Tyler Durden was wrong; you are your fucking khakis. The stuff you own—whether you buy it, inherit it, or receive it as a gift—can reshape the way you think about yourself.

“By owning something, we not only receive control of it but, ironically, we also surrender control to it, allowing it some influence over our self-evaluation and behavior,” says Liad Weiss, PhD, a professor of marketing at the University of Wisconsin and coauthor of a new study that demonstrates all the ways the stuff you own can mess with your self-image.

In one of Weiss’s more straightforward experiments, people who were gifted tall, narrow coffee mugs reported feeling taller and having higher self-esteem. People who received a shorter, fatter mug felt just the opposite. More of Weiss’s research suggests owning an item from a brand you associate with dishonesty (Volkswagen, anyone?) can actually make you feel and act more dishonestly.

Just as your job, your partner, and your friends influence the way you see yourself, the stuff you own seems to have the power to pump up or deflate your self-image, Weiss says.

But ownership is the key, he says. If you borrow or rent an item, you’re aware that it’s not your property. That sense of non-ownership can make you to feel as though its characteristics aren’t a part of your self-image, he explains.

If that’s confusing, here’s an example: In another mug experiment, people who were told they could borrow (but not keep) a tall coffee cup reported feeling shorter after using it, Weiss says.

When you think about it, all this makes a lot of sense. You’d never admit it to anyone, but when you drop cash on a new item—whether it’s a necktie or a new car—you can’t help seeing that object as a representation of yourself. (The entire world of consumer marketing is built on this concept.)

So what’s the takeaway? Be careful about buying stuff or accepting items that don’t mesh with your self-image. If you pass on the watch you really want in favor of a cheap knockoff, that purchase could make you see yourself as economical—or as a penny-pinching fake, Weiss’s research indicates.

Likewise, be wary of holding onto stuff that doesn’t fit the way you see yourself. That ugly shirt your ex gave you? Or that POS bike you picked up when you were a broke college kid? You might be surprised how much getting rid of both improves the way you feel about yourself. “Sorting through possessions and discarding ones that are inconsistent with your self-evaluation is a good way to literally and metaphorically get rid of old baggage that you carry with you from your past,” Weiss says.

At the same time, you don’t have to stress about every minor purchase or gift. Weiss says big ticket items—stuff like your car or your home, which are more likely to stay “top-of-mind”—are likely to have a stronger and more lasting effect on how you see yourself.