For the liar, telling a lie has obvious costs. Keeping track of the lies one tells and trying to maintain the plausibility of a fictional narrative as real-world events intrude is mentally taxing. The fear of getting caught is a constant source of anxiety, and when it happens, the damage to one’s reputation can be lasting. For the people who are lied to the costs of lying are also clear: Lies undermine relationships, organizations and institutions.

However, the ability to lie and engage in other forms of deception is also a source of great social power, as it allows people to shape interactions in ways that serve their interests: They can evade responsibility for their misdeeds, take credit for accomplishments that are not really theirs, and rally friends and allies to the cause. As such, it’s an important step in a child’s development and there are cognitive building blocks that must be in place in order to successfully lie.

One way research psychologists have sought to understand the reasoning behind the choice to lie versus tell the truth is to go back to when we first learn this skill in childhood. In some studies, researchers ask children to play a game in which they can obtain a material reward by lying. In other studies children are faced with social situations in which the more polite course of action involves lying instead of telling the truth. For example, an experimenter will offer an undesirable gift such as a bar of soap and ask the child whether he or she likes it. Yet another method is to ask parents to keep a written record of the lies that their children tell.

In a 2017 study, my colleagues and I sought to understand children’s thinking processes when they were first figuring out how to deceive other people, which for most children is around age three and a half. We were interested in the possibility that certain types of social experiences might speed up this developmental timeline.

Watching children discover how to deceive

We invited young children to play a simple game they could win only by deceiving their opponent: Children who told the truth won treats for the experimenter and those who lied won treats for themselves.

In this game, the child hides a treat in one of two cups while an experimenter covers her eyes. The experimenter then opens her eyes and asks the child where the treat is hidden, and the child responds by indicating one of the two cups. If the child indicates the correct cup, the experimenter wins the treat, and if the child indicates the incorrect one, the child wins the treat.

Children played 10 rounds of this game each day for 10 consecutive days. This method of closely observing children over a short period of time allows for fine-grained tracking of behavioral changes, so researchers can observe the process of development as it unfolds.

We tested children around the time of their third birthday, which is before children typically know how to deceive. We found that, as expected, when children first started playing the game most of them made no effort to deceive, and lost to the experimenter every time. However, within the next few sessions most children discovered how to deceive in order to win the game – and after their initial discovery they used deception consistently.

Just one developmental milestone

Not all children figured out how to deceive at the same rate. At one extreme, some figured it out on the first day; at the other extreme, some were consistently losing the game even at the end of the 10 days.

We discovered that the rate at which individual children learned to deceive was related to certain cognitive skills. One of these skills – what psychologists call theory of mind – is the ability to understand that others don’t necessarily know what you know. This skill is needed because when children lie they intentionally communicate information that differs from what they themselves believe. Another one of these skills, cognitive control, allows people to stop themselves from blurting out the truth when they try to lie. The children who figured out how to deceive the most quickly had the highest levels of both of these skills.

Our findings suggest that competitive games can help children gain the insight that deception can be used as a strategy for personal gain – once they have the underlying cognitive skills to figure this out.

It’s important to keep in mind that the initial discovery of deception is not an endpoint. Rather, it’s the first step in a long developmental trajectory. After this discovery, children typically learn when to deceive, but in doing so they must sort through a confusing array of messages about the morality of deception. They usually also learn more about how to deceive. Young children often inadvertently give away the truth when they try to dupe others, and they must learn to control their words, facial expressions and body language to be convincing.

As they develop, children often learn how to employ more nuanced forms of manipulation, such as using flattery as a means to curry favor, steering conversations away from uncomfortable topics and presenting information selectively to create a desired impression. By mastering these skills, they gain the power to help shape social narratives in ways that can have far-reaching consequences for themselves and for others.