I spend way too much time thinking about the Doughnut Vault. For one thing, it’s so temptingly close. If I get off the train at the Merchandise Mart stop in the morning and take the stairs down to the street instead of dutifully marching into the Mart, toward the office, it’s just a block away.

For another, there’s the Twitter feed that keeps followers apprised on doughnut availability throughout the morning, so easy to access from a smartphone, especially if you’re riding the Brown Line and are superbored. 9:45 AM, passing Sedgwick: “4 dozen vanilla, 2 dozen chocolate, 1 dozen chestnut, 4 dozen buttermilk old fashioned, 2 dozen pineapple old fashioned, half a dozen gingerbread stacks left. 10 people in line.”

Oh, the suspense! The mental calculation! How acquisitive are these potential doughnut buyers? Do they want a single sinker with their coffee, or are they buying for a whole office, or are they visiting doughnut aficionados who have read about the Doughnut Vault in some foodie magazine and have traveled long distances to try every single one?

So far, the magical convergence of factors—a doughnut-eating mood, doughnut availability, and cash in wallet (the Doughnut Vault does not accept plastic)—has happened for me only once. It was a pretty good doughnut. But still, I keep thinking about the Doughnut Vault. And about my high school economics class and the principle of supply and demand.