A YEAR AGO this month my friend Sally decided to go a year without buying clothes.

A successful entrepreneur, wife, and mother with a professional history in advertising and fashion and a personal history as daughter of a retail executive who said things like, "You won’t want to be caught dead in those jeans next season!"—she knew it would be tough.

She also knew it was time. "I was grossed out by the economy, by the fact that I was buying clothes on impulse that I didn’t need or even really want," she told me, her signature character blend—one part princess, three parts principled—on winning display. With characteristic chutzpah Sally whipped up a blog—thegreatamericanappareldiet.com —and recruited a corps of fellow "dieters" to abstain from buying clothes September 1, 2009 to August 30, 2010, while blogging about their experiences. Since its launch the list has grown to some 138 women—and two men—from around the globe.

Clothes could be swapped or handed down. New shoes, accessories, and undergarments were allowed. "Had to have something," Sally confessed. "And, I mean . . . undies." But no new clothes. Nada. Zip. Not even unzip.

And so on Day 284 of the Great American Apparel Diet, Sally and I stood in Barneys. I was there to find out what she’d learned, figuring that if she could tell me in Barneys, T minus 80 days till the end of the diet—she must have really learned it.

Lesson #1: Not buying any clothes for a year is really, really hard. Three months in, she was the picture of insouciance—still stylish in the fall clothes she’d stocked up on before the diet, still having fun reinventing combinations from her enormous collection.

Come May—different story. She’d cheated twice. (Once on pajamas—"perimenopausal night sweats ruined mine"—and once on yoga pants she bought at the gym after forgetting her own.)

Crossing the bar into springtime was hardest, when new fashions started filling the stores and Sally’s friends had the nerve to start buying them. One night she left the house all cute in her put-together ensemble but returned feeling frumpy and pissed off. In between she’d gone to a party with her most fabulous friend, a coffee industry exec whose trips to New York and Asia kept her impeccably, creatively garbed. "I came home and thought, ‘I hate this diet,’ " she grumbled. "That was my low point."

Lesson #2: Having a full closet doesn’t make it easier. Like Sally, many of the dieters started out believing they owned enough clothes to last a long time. They found that life in one’s own closet grows tedious fast. "I learned that it’s not about how many clothes you have; it’s about reinventing yourself with new ones," she told me. "It’s like being a painter and having only five colors."

Lesson #3: Shopping’s not so much about getting new clothes as it is about creating identity. If she’s learned anything, it’s that clothes tell the story of who we are. "Shopping," Sally sighed, "is so much more than shopping."

Complicating that fact have been the unique circumstances of a year in which she worked from home and felt the onset of midlife. "It’s like adolescence revisited," she said. "I’m not entirely sure what I’m trying to look like," she admitted, fingering a Barneys filigreed lace top with bold front zipper. "I am sure I don’t want to start shopping at Chico’s."