“If you’re looking for minimalism at the donation door, you’re not seeing it — people are donating just as much stuff as before,” because they’re still buying new things that eventually end up in a donation bag, said Adam Minter, the author of “Secondhand: Travels in the New Global Garage Sale,” a book about a vast global market of used items fueled by the stuff people no longer want. Mr. Minter described the American donation frenzy of 2019 as “a brief cultural phenomenon” with no lasting impact on the secondhand market.

Clutter is particularly stressful for women, who are often the ones tasked with keeping the home orderly, said Dr. Saxbe, of the University of Southern California, where she is an associate professor of psychology.

Yet, we go out and buy more stuff anyway. Dr. Saxbe sees two forces at play. Shopping satisfies a natural urge to forage — we feel good when we collect things for our family. But maintaining a calm, orderly household is extremely difficult in a culture that provides families with little support, and so we feel frazzled. “We satisfy our stress by going out and consuming, because it is something that makes us feel better,” she said. “And that’s very ironic because it can make us feel very overwhelmed.”

Resisting the urge to bring new things home is hard, even if you’ve made a conscious choice to live smaller. Last April, Gabriela Nuñez moved with her partner, Angel Orozco, and their young son from a three-bedroom condo in Orange County to a 677-square-foot, one-bedroom apartment in Los Angeles. They wanted to live closer to the coffee shop that Mr. Orozco, 45, co-owns. Downsizing meant reducing the family’s possessions by a third — a long, grueling process. But Ms. Nuñez, 43, was resolute, enlisting friends to help her open boxes and make hard choices.

Then came the holidays. Ms. Nuñez, an associate professor of Chicano and Chicana Studies at California State University at Fullerton, briefly forgot about her new slimmed-down lifestyle and indulged in new clothes for herself and gifts for her family. She struggled to convince friends and family that she simply did not have room for presents. “The holidays are really hard for me because I just get caught up in it all,” she said. “I get into buy mode.”

Now, with the holidays over, she’s facing the reality that she has to clear out her closets once again, this time to make room for all her new possessions. The process has brought up uncomfortable feelings about why she shops. “I have no problem getting rid of stuff, but I can think of five things that I want to buy today,” she said. “I’m trying to be honest about that and change that.”