In the days ahead, managers and employees of the Hyatt hotel chain will be doing favors for some of their customers. Maybe they always did them, but these favors will be different: they will be what Hyatt Hotels’ C.E.O., Mark Hoplamazian, has called “random acts of generosity,” like unexpectedly picking up the tab for your hotel-bar drinks or hotel-spa massage. “Random” seems slightly off as a description, in that Hoplamazian announced this pending outburst of hospitality, and the months of consumer research that preceded it, in a guest post on a USA Today business-travel blog. But the idea is that the unexpected nature of the gifts will leave the customer not just pleased but also grateful. Gratitude is a powerful, and potentially quite profitable, emotion to inspire.

A coming paper in the Journal of Marketing addresses that very subject. Building on past research on the role of gratitude in human relationships, it argues that a customer who is made to feel grateful most likely becomes enduringly loyal as a result. Gratitude, as the paper bluntly puts it, can “increase purchase intentions, sales growth and share of wallet.” Robert Palmatier, an associate professor of marketing at the University of Washington and an author of the paper, says that making a customer feel truly grateful toward a business is harder than it might sound. And the hard-wired feelings of reciprocity that can trigger gratitude can just as easily trigger the sense that you’re being treated unfairly.

The most familiar form of “relationship marketing” (that subset of selling tactics that revolve around maintaining repeat business from regular customers) is probably the so-called loyalty program. Frequent-flier miles, for instance. Hyatt, like many big hotel chains, already has such a program: Hyatt Gold Passport members who rack up enough “points” by staying at its properties can get a free night in a hotel. Nobody feels gratitude in this setup; in fact, points and miles are invariably referred to as something you earn.

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While Palmatier says there has been a lot of research on the psychology of gratitude in the past five or six years, he points to an older study that’s now considered a classic. Participants waiting for an experiment to begin were treated in one of two ways: Some were unexpectedly given a soft drink by an assistant posing as another participant, and others were not. This seemed like an act of pure generosity on the part of a fellow participant, but it was actually part of the experiment. When the same assistant later asked subjects to buy raffle tickets, those who had been given a soda were far more likely to do so — and on average bought twice as many tickets as those who didn’t get a soda. This says something about the human animal, and Palmatier adds that other studies have found that we feel pleasure from reciprocating out of gratitude, and guilt when we don’t. This, he adds, is something a business can use to its advantage or, depending on how you look at it, exploit.