Getting a parking space at your average Trader Joe’s on any given Wednesday at 5pm requires the persistence of the hedgehog and the wiliness of the fox (here’s Buzzfeed’s recent roundup of Twitter frustration). But UCLA professor Donald Shoup, who has risen to cult-figure status among urban planning nerds for his book-length condemnation of free parking, tells CityLab that TJ’s tiny lots illustrate an uncomfortable but universal truth.

“Just because parking is free doesn’t mean no one has to pay for it,” says the septuagenarian sometimes known as Shoup Dogg.

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Trader Joe’s takes advantage of that fact. By keeping their stores and parking lots small, the grocer lowers overall costs, helping you get (to choose my two favorite examples) soy chorizo for $1.99 and a bottle of recognizable cabernet sauvignon for three bucks. The densely arranged stores also help them get more than double the sales per square foot of competitors.

It’s not that customers are exactly complaining that Trader Joe’s stores have no parking – those stores have to meet whatever standards local ordinances set. But they often offer just the minimum, meaning customers might have to wait for spaces, or pay for off-site parking. Shoup’s broader thesis is that if even less parking were free, subsidized by cities and development codes, we’d make more thoughtful decisions about transportation, and we’d live in nicer, less asphalt-y towns.

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“It’s the American expectation that’s creating the problem,” says Shoup. “The expectation that there will be free parking and plenty of it, and if there isn’t, there’s something wrong.”

To see what he means, look at the huge parking lots of your Ikeas, Wal-Marts WMT , or Whole Foods WFM . As shown by the annual Black Friday Parking project, those lots are often half-empty even on the biggest shopping day of the year. Every time you look at those empty spaces, remember—they’re costing you.