One reason Black Friday exists:
Some people delight over the idea of fighting over the last Nintendo Wii, or whatever the item of the year happens to be. This study found that "perceived competition … creates positive emotions and induces hedonic shopping value." Black Friday creates that kind of "perceived competition" in that it's not just a shopping day with a bunch of people. It's a shopping day with a bunch of people where discounts don't last and discounted products are scarce. "At certain levels, consumers enjoy arousal and challenges during the shopping process," researcher Sang-Eun Byun told The Washington Post's Olga Khazan. "They enjoy something that’s harder to get, and it makes them feel playful and excited." Given that bit of science, it's no wonder that shoppers have acted quite aggressive in recent years, as this Christian Science Monitor article notes.