In her research, Dr. Nichols has found that scarcity sparks “consumer competitive arousal,” the belief that a consumer situation is a competition in which there are potential “winners” and “losers.” Similar feelings arise at auctions, she said. “People want to feel they got a good deal,” she said.

Competitive arousal can be ignited by a perception that a specific good, such as a popular toy or flat-screen television, is in limited supply and available for only a short period of time. Dr. Nichols found in her research, for example, that video game consumers had a heightened competitive arousal after viewing advertisements that described a new game as scarce or in limited supply.

“With Black Friday, those stampedes are driven by the emotions that are drawn from scarcity and competition,” Dr. Nichols said.

Competitive arousal can bring about another emotional driver: bonding. Dr. Nichols has extensively studied the former “running of the brides” at Filene’s Basement stores in Atlanta, Chicago and Washington, in which designer bridal gowns were drastically reduced in price. At the event, brides-to-be, joined by friends or family members, teamed up to grab as many dresses as possible for the bride to consider.

“In the beginning, they expressed the mind-set that they wanted to ‘win,’ by finding a $5,000 dress for $300,” Dr. Nichols said. “But in the end, the dress became ancillary. The experience was about competing and bonding together.”

Sharing the Black Friday ritual with friends and family can create a similar sense of tribal bonding, Dr. Nichols said, and reinforce bad behavior. In one of her ‘running of the brides’ studies, the shoppers revealed how they hoarded as many dresses as possible, and negotiated trades with other shopping teams in which they misrepresented the value of the gown they gave away.

“Some admitted, ‘I was walking by a group of girls and they weren’t looking, so I took three of their dresses,’” Dr. Nichols said. “They felt like it was part of the game and it was acceptable to do these things. They thought, ‘I competed well.’”