With more people shopping online, Black Friday has become better known for the wild and crazy fights that break out in stores across the nation than for the steep discounts shoppers can get on a limited amount of 58-inch LED TVs. Some of these fights don’t even start inside the stores, but in the crowds outside, and a quick YouTube search will turn up videos of the tense atmosphere. Why is there so much tension when shoppers haven’t even gotten inside yet? According to a new study, this happens because we often assume everyone else wants exactly the same thing as us, even if they don’t.

The new research highlights how inherently competitive humans are. As we attempt to reach a goal, our brains automatically assume others are trying to reach it, too — a psychological effect called “goal projection.” Researchers from New York University found that the more a person was determined to reach their goal, the more likely they were to project their own goals onto others.

“If we’re fixated on seeing that blockbuster film or purchasing those fresh strawberries, we’re more likely to see others wanting to do the same,” said Janet Ahn, an NYU doctoral candidate, in a press release.

Ahn and her team of researchers looked at how people perceived others before seeing a film at a theater, how they perceived others at a busy train station, and both before and after grocery shopping in a Whole Foods Market. The team approached people who were about to buy tickets to a movie, and asked them to gauge their “goal commitment” on a scale of 1 (not at all) to 5 (extremely). They asked participants, “How badly do you want to watch this movie?” Participants who expressed a stronger wish to see the movie were more likely to assume someone waiting at the front of the ticket line was also going to see the same movie.

Next, the researchers asked travelers at New York’s Penn Station to gauge how strongly they wanted to go home, and then asked them how likely a random person in the station was to be going to the same destination. They did this to see how much a person’s goal (getting home) was associated with their perceived similarity to others, and found people who were most in a rush to get home were more likely to see the other person as similar.

Finally, in a third experiment, they asked people who were both leaving and going into a Whole Foods to gauge how committed they were to buying a specific item — the difference being that the group leaving had already gotten their item. Then, each participant was asked how similar they felt to a random person going into the store, and how likely it was that the person would buy the same item. Again, participants who rated the person as more similar also thought they were looking for the same item. Meanwhile, those who had already gotten what they needed saw the person as less similar and less likely to look for the same item.

“This suggests there is a competitive aspect to goal projection — we think others are after the same things if we have yet to obtain them,” Ahn said. And chances are this is also the reason Black Friday crowds are so tense before the store’s doors open. To one person’s mind, everyone else is trying to get the same thing.

Source: Ahn J, Oettingen G, Gollwitzer P. Goal projection in public places. European Journal of Social Psychology. 2015.