One of my grandfathers was the manager of a huge department store in Buffalo, NY called Flint & Kent. This was a store like City of Paris or I. Magnin's in San Francisco used to be, before department stores branched out and diluted themselves, before you could find a Nordstrom's in every shopping mall with the right zip code in America. Since he died when I was seven, what I know about him comes from stories my dad told me.

My grandfather used to give lectures about retailing at business schools on the East Coast, and was famous for the way he talked about a retailer's year. First, he would say, you pay your rent. That's where all your earnings go until late May. Then you pay your sales staff, your administrators, your utility bills. By this time it's the end of July. All of August covers your advertising, and in early September you begin to pay for the whole year's inventory. Then he would pause and smile at his students. At 4 p.m. on Christmas Eve, you have paid off your expenses for the entire year. From 4 to 10, or whenever you decide to close the shop, that's your profit.

I love this story because of how it deflates the idea of making easy money. Instead of thinking about selling a fur coat, say, at the usual keystone mark-up (which means double) for $2000 and imagining you can make a clear thousand on it, he put the selling of that fur coat into its proper context, alongside the rent on the four square feet of display space it would take up, the proportion of salespeople's paychecks, how much the ads cost, the heat, the air conditioning, what tiny part of the salary of the guy at the white baby grand on the mezzanine this fur coat would have to carry.

After I got out of college and had knocked around for a couple of years, I worked in retail for a small store in Cambridge, selling and managing and later buying. I used to look out at Brattle St. on snowy December afternoons and think about my grandfather's story, imagining the bright lights of Flint & Kent, the store lit up like an ocean liner moored in downtown Buffalo. And think of the bustle and rush as Christmas got closer and closer, and my grandfather walking through the aisles, noticing things, tweaking a hanger here and there, making jokes with his staff, drinking a little eggnog with the piano player.

And in many holiday seasons since, even though I try hard to make things instead of buying them, I have found myself out in the fray on Christmas Eve afternoon, as though a bell had rung inside my head. It's a crazy time to try to shop. People are out of their minds. But I want to be part of the throng, to feel that urgency of humanity: gaiety mingled with panic under the colored lights.

And I can see my grandfather's smile. It's 4 p.m. Everything from here on out is profit.