In the modern era, it seems probable that the way people now shop online for goods—in virtual marketplaces, where they can easily filter out features they do and don’t want—has influenced the way people “shop” for partners, especially on dating apps, which often allow that same kind of filtering. The behavioral economics researcher and dating coach Logan Ury said in an interview that many single people she works with engage in what she calls “relationshopping.”

Read: The rise of dating-app fatigue

“People, especially as they get older, really know their preferences. So they think that they know what they want,” Ury said—and retroactively added quotation marks around the words “know what they want.” “Those are things like ‘I want a redhead who’s over 5’7”,’ or ‘I want a Jewish man who at least has a graduate degree.’” So they log in to a digital marketplace and start narrowing down their options. “They shop for a partner the way that they would shop for a camera or Bluetooth headphones,” she said.

But, Ury went on, there’s a fatal flaw in this logic: No one knows what they want so much as they believe they know what they want. Actual romantic chemistry is volatile and hard to predict; it can crackle between two people with nothing in common and fail to materialize in what looks on paper like a perfect match. Ury often finds herself coaching her clients to broaden their searches and detach themselves from their meticulously crafted “checklists.”

The fact that human-to-human matches are less predictable than consumer-to-good matches is just one problem with the market metaphor; another is that dating is not a one-time transaction. Let’s say you’re on the market for a vacuum cleaner—another endeavor in which you might invest considerable time learning about and weighing your options, in search of the best fit for your needs. You shop around a bit, then you choose one, buy it, and, unless it breaks, that’s your vacuum cleaner for the foreseeable future. You likely will not continue trying out new vacuums, or acquire a second and third as your “non-primary” vacuums. In dating, especially in recent years, the point isn’t always exclusivity, permanence, or even the sort of long-term relationship one might have with a vacuum. With the rise of “hookup culture” and the normalization of polyamory and open relationships, it’s perfectly common for people to seek partnerships that won’t necessarily preclude them from seeking other partnerships, later on or in addition. This makes supply and demand a bit harder to parse. Given that marriage is much more commonly understood to mean a relationship involving one-to-one exclusivity and permanence, the idea of a marketplace or economy maps much more cleanly onto matrimony than dating.

The marketplace metaphor also fails to account for what many daters know intuitively: that being on the market for a long time—or being off the market, and then back on, and then off again—can change how a person interacts with the marketplace. Obviously, this wouldn’t affect a material good in the same way. Families repeatedly moving out of houses, for example, wouldn’t affect the houses’ feelings, but being dumped over and over by a series of girlfriends might change a person’s attitude toward finding a new partner. Basically, ideas about markets that are repurposed from the economy of material goods don’t work so well when applied to sentient beings who have emotions. Or, as Moira Weigel put it, “It’s almost like humans aren’t actually commodities.”