gratitude
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Be grateful. That's been my science-backed mantra for a good many years. I say science-backed because unlike the rationale your parents relied on when urging you to be appreciative (though they were right!), my advice comes from more than a decade of accumulating empirical evidence showing that gratitude makes life better.

But while it can help combat stress and depression, improve your diet, and even get you to the gym, perhaps one of the most important ways gratitude improves life is through fostering cooperation — a phenomenon so integral to human existence that we would have been hard-pressed to achieve much of what we've accomplished as a species without it.

Cooperation, at base, requires people to share resources over time in order to obtain something that would have been impossible, or at least more difficult, to get on their own. Yet the benefits that arise from sharing knowledge, money, or even elbow grease come with an important caveat: you only get them if your partners are fair.

When it comes to cooperation, it takes two to tango, and if your partners regularly turn out to be cheats, your outcomes will be poor. So when I touted the benefits of gratitude, I had a worry lurking in the back of my mind that I couldn't shake. While it's certainly true that feeling grateful makes people more generous and more honest — both essential features for fostering cooperation — it might also have a downside: Was I setting people up to be suckers?

You see, gratitude, like all emotions, subtly shapes the mind's expectations. And unless we're actively on the lookout to correct for an emotion's influence — a nudge that we usually don't recognize in the moment — we tend to behave in line with it. When it comes to gratitude, that can mean a push toward being blindly cooperative.

Along these lines, a good deal of research confirms that people who feel grateful are certainly attractive to work with. For example, we've repeatedly shown that gratitude makes people not only more willing to repay debts or favors to previous benefactors, but also to pay such favors forward to strangers — a tendency that goes a long way toward increasing cooperation in a group. The upshot, then, is pretty clear: if you want to find a reliable partner with whom to work, look for one who regularly feels grateful. It's a signal she'll be trustworthy. Yet there's the rub. She'll be trustworthy, but will all of her partners?

The clear signal of honest, generous intent that comes with feeling and expressing gratitude can cut both ways. Having more "cooperators" in a group means there are more opportunities for these good people to work together. But it also means there are more opportunities for bad actors to exploit and, consequently, that some individuals will get the shaft.

Consider this thought experiment that I've adapted from one my collaborator Robert Frank often uses. Imagine you — a trustworthy person — walked around with a big T on your forehead signaling such. You'd be a popular partner choice, both for those who are, like you, well-intentioned and for those who would see you as an easy mark — one who would gladly offer resources with which they could abscond. If you had no easy way to accurately determine a potential partner's intent, you'd often be in a pickle. Might feeling and expressing heartfelt thanks be similar to that big T?

There's some reason to think it might be. For example, Jeremy Yip and colleagues found that within the context of competitive negotiations, those who express gratitude are seen as an easy target. In a series of studies, Yip's team demonstrated that people often make more aggressive, self-interested offers when negotiating with someone who showed gratitude after an initial offer, because they think they'll be easier to exploit without repercussion.

What they fail to realize, though, is that when interactions aren't one-offs, grateful people aren't suckers. They're not complacent. They expect more moral behavior not only from themselves but from others. And it's here, in the realm of punishment, that gratitude can prevent repeated exploitation.

Third-party punishment — a phenomenon where one person will punish another for transgressions against a third person — has been shown within both lab and real-world contexts to limit exploitation and free riding. Simply put, when punishment is likely, more people tend to fall in line. And while, at first blush, it might seem counterintuitive that a positive emotion like gratitude might motivate people to punish transgressors in this way, our newest work proves the point.

In two experiments, we adapted a methodology used by Ernst Fehr and colleagues wherein we endowed our participants with money and then asked them how much of that endowment, if any, they'd spend to punish another person who made different degrees of unfair splits in a dictator game (a game wherein one person is given money and is free to decide whether to share any of it with a partner).

To make the stakes real, we also told them that we'd honor one of their choices at random. That is, we'd subtract the amount of money they indicated from their endowment. The catch was that just prior to making these decisions, we induced people to experience gratitude, happiness, or a neutral emotional state. Across the splits, a clear pattern emerged: those feeling grateful spent about 10 percent more to punish selfish "dictators." Those feeling happy spent the same to punish as did those feeling neutral, thereby showing that the increase in punishment didn't simply result from any positive feeling.

This propensity for gratitude not only to nudge people to behave fairly but also to punish others who don't offers a remedy for one of gratitude's potential problems. By helping to ensure a price will be paid for cheating down the line, it stands as a check on continued exploitation. And in so doing, eases the worry that has long plagued me. Grateful people do make good peers and partners. But if exploitation occurs, they won't sit idly by.