We tend to trust the people around us. We trust cab drivers and doctors with our lives, we trust chefs handling our food, and we trust strangers to watch our belongings while we step away. But trust is not like candy on Halloween, we do not just give it to anyone who knocks on our door. Psychologists have long been interested in understanding what leads people to trust others, and the face has long been at the center of this research. Some people just look trustworthy. Faces that look happy even when not smiling and those that have feminine and even baby-like features tend to be trusted more. Yet, just because a face looks trustworthy does not mean that the person with that face has trustworthy intentions.

A recent paper suggests that it isn’t easy to accurately detect another’s trustworthiness from just the face, but a few things can help. We can more accurately judge trustworthiness if we get a chance to interact with the person, or at least observe a video of the person. Some research finds that even from observing photographs of faces, judgments of trustworthiness can have a glimmer of accuracy, but other research casts doubt on this idea.

At Columbia Business School, my colleague and I were taken by this question, but felt that something had been missing. Many studies had asked whether people can accurately detect trustworthiness from the face, but not a single study had ever asked what the person with the face thought about all of this.

We wondered whether people who look trustworthy are aware that other people expect them to be trustworthy from their appearance. In essence, we turned the question around, and held it up to a mirror, asking: Does the person with a trustworthy or untrustworthy looking face think that they will be trusted or distrusted by others? If this were the case, it could explain how people can sometimes accurately judge another’s trustworthiness from the face. And so, we tested this new idea.

In a recent paper, we asked people to play a new economic game we developed. In most economic games, to trust the other player requires that you also cooperate with them. For example, in one classic economic game, a player receives money, which they can send to another player, and whatever is sent triples in value. To cooperate and send them money implies you hope you can trust them to send some back. Our game, however, had a unique feature where both players had to decide whether or not to tell the truth, and both players had to decide whether or not to trust the other player. This allows one player to lie to the other player, but still trust them. In other words, our game separated cooperating from being trustworthy. After explaining the game to the participants, we asked them to guess how often they thought other people would trust them in the game. They then played the game 10 times, with 10 unique people, and there were cash prizes for the winners.

It turns out that the more a person’s face looks trustworthy (as rated by a separate group of people), the more the person with that face predicted that other people would trust them. People have a sense of how trustworthy they look. And here’s where things get even more interesting. In our game, being trusted while lying was by far the most profitable outcome. And yet, the very people who look trustworthy do not want to exploit that trust for monetary gain, and so they told the truth the most. People want to live up to other people’s expectations.

A recent study conducted in China on children’s faces replicated our effects and took them one step further. The researchers had people judge how trustworthy 8-12 year-old’s faces appeared to be, and found that the more trustworthy the children looked, the more their peers accepted them, and the more, in turn, the children behaved in a kind, trustworthy manner. When children looked trustworthy, other children expected them to be kind, and therefore treated them kindly, which even a year later predicted how trustworthy those children, in turn, acted in class.

When people can accurately judge another person’s trustworthiness, they are helped, in part, by the person with that face. That person knows they look trustworthy (and that others expect them to be trustworthy) and doesn’t want to let other people down. Unfortunately, the flipside of this is that for those with less than trustworthy-looking faces, if they think that other people won’t trust them, they might feel more inclined to bend the truth. People tend to live up to the best, and the worst, of what is expected of them. And so, recognize the power of your own expectations. If you give people a positive expectation to live up to, you have a better chance of bringing out the best in them.