A few years ago, my mom brought me to one of those sales for special designer collaborations at Target. At 6:30 a.m., we drove to a big store in suburban Maryland, then stood in line in the early spring chill, chatting pleasantly with the other would-be shoppers, mostly women in their 30s and 40s. My mom whispered her game plan to me in line (plotting which areas of the store we should run to first based on the items we had looked at online the night before, contingency plans if the items were not concentrated as she had hoped but instead throughout the store), but it didn’t register so well before my first cup of coffee. As soon as they threw open the doors at 8 a.m., the dynamic shifted dramatically — the game was on. Women started shoving past each other, throwing their elbows, running for the remaining garments on the shelves. I was quickly pushed to the side — I couldn’t compete. My mom, however, moved like a fish in water, valiantly grabbing the dress she knew I wanted instead of the shoes she wanted. That’s real maternal sacrifice. By 8:20 a.m., the racks were empty.

This type of scene, though foreign to some, is not uncommon — it happens periodically when finite, coveted items such as fancy sneakers go on sale, or every year on Black Friday. It doesn’t seem to matter that most of these items are available online, anyway. What happens to turn mild-mannered suburbanites into aggressive shoppers, and what distinguishes the battle-ready from the bystanders?

“Shopping is not just a functional activity, but sometimes a therapeutic activity. A lot of people who shop don’t do it because they need stuff,” says Mario Campana, lecturer in marketing and consumer behavior at the University of London.

Shopping in this kind of high-pressure setting for limited-availability goods — otherwise known as competitive shopping — is fundamentally different than, say, waiting politely in line for the new iPhone. It’s really not about the stuff at all; it’s about winning. “It’s like playing a game of tennis, or any other sport,” says Kit Yarrow, professor emeritus of psychology and marketing at Golden Gate University. “Competition is enjoyable for people. It taps into our most primal instincts for survival.”

People may initially be drawn to sales like these if a friend or loved one brings them along, or if they are particularly interested in the items on sale. But like any sport, people become more interested in it if they find they are good at it. Though typically women shop more than men, it’s not just women who enjoy it, or who react to it competitively (in fact, men make up a larger proportion of Black Friday shoppers, according to a 2016 study). Competitive shoppers hone their skills, develop strategies, and plan in advance, Yarrow says. For them, it’s a fun social activity, though Yarrow admits that it can be incomprehensible and “like hell on earth” to people who aren’t into it.

Part of the fun is that the activity, unlike much of what we do, isn’t really a mental one. The neuroscience of these events hasn’t been studied much, but to anyone who has experienced it, it seems obvious that the frenzied rush for goods triggers the “fight or flight” response, releasing adrenaline that causes the heart to beat faster, the airways to open, and the senses to sharpen while disengaging the rational mind (the one that worries about abstract things like work or relationships). That creates “a little vacation” from our usual thoughts, Yarrow says, allowing us to focus on the moment the way a sport can if you’re “in the zone.” “The escape is part of the allure,” Yarrow adds. “Though they might have that initial planning and prep, once [shoppers] get into the heat of battle, any normal household worries or relationship worries tend to disappear, replaced by the thrill of victory.”

That anticipatory buildup also causes the brain to release dopamine, part of the reward system. That good feeling is conditioning shoppers to want to do it again. Plus, victors have a nice new item to take home; the defeated, well, at least they have a good story.

Most of the people drawn to sales are looking for this very normal kind of release and reward. But there are also some who are thrill-seekers or compulsive shoppers, have poor impulse control, or have issues with anger or aggression, sometimes even to problematic levels, says Frank Farley, a professor of educational psychology at Temple University and former president of the American Psychological Association. Psychological phenomena called social facilitation and emotional contagion can work in tandem to turn a crowd into a riot with only a few of these folks in the mix. Farley describes it like this: “You have a crowd. Someone does something, they push someone. It arouses the emotion in general, and you get this contagious effect. There’s literally a piling on of bad behavior.” We’ve all seen the effects that can have, either at Black Friday sales that turn deadly or when post-Super Bowl celebrations lead to property damage.

The intensity of the competitive shopping experience (assuming it didn’t get ugly) means that these types of sales will likely continue, even as more of our shopping moves online. Online auction sites are exciting, but they lack the social element of these real-life sales. “Our online worlds in so many ways are deadening. These lively in-person exchanges are even more exciting than they used to be; we spend so much time with this somnambulistic state in online shopping,” Yarrow says.

“I’ve spent decades studying human nature, and in my view it doesn’t change radically over time,” Farley says. Even if the number of sales decreases, he adds, the things that they bring out in us, both good and bad, will find new venues to show themselves.