Let’s start with a question, which might be the oldest question of all: Why do certain groups add up to be greater than the sum of their parts, while others add up to be less?

A few years ago the designer and engineer Peter Skillman held a competition to find out. Over several months, he assembled a series of four-person groups at Stanford, the University of California, the University of Tokyo, and a few other places. He challenged each group to build the tallest possible structure using the following items:

The contest had one rule: The marshmallow had to end up on top. The fascinating part of the experiment, however, had less to do with the task than with the participants. Some of the teams consisted of business school students. The others consisted of kindergartners.

The business students got right to work. They began talking and thinking strategically. They examined the materials. They tossed ideas back and forth and asked thoughtful, savvy questions. They generated several options, then honed the most promising ideas. It was professional, rational, and intelligent. The process resulted in a decision to pursue one particular strategy. Then they divided up the tasks and started building.

The kindergartners took a different approach. They did not strategize. They did not analyze or share experiences. They did not ask questions, propose options, or hone ideas. In fact, they barely talked at all. They stood very close to one another. Their interactions were not smooth or organized. They abruptly grabbed materials from one another and started building, following no plan or strategy. When they spoke, they spoke in short bursts: “Here! No, here !” Their entire technique might be described as trying a bunch of stuff together .

If you had to bet which of the teams would win, it would not be a difficult choice. You would bet on the business school students, because they possess the intelligence, skills, and experience to do a superior job. This is the way we normally think about group performance. We presume skilled individuals will combine to produce skilled performance in the same way we presume two plus two will combine to produce four.

Your bet would be wrong. In dozens of trials, kindergartners built structures that averaged twenty-six inches tall, while business school students built structures that averaged less than ten inches. ^*1

The result is hard to absorb because it feels like an illusion. We see smart, experienced business school students, and we find it difficult to imagine that they would combine to produce a poor performance. We see unsophisticated, inexperienced kindergartners, and we find it difficult to imagine that they would combine to produce a successful performance. But this illusion, like every illusion, happens because our instincts have led us to focus on the wrong details. We focus on what we can see—individual skills. But individual skills are not what matters. What matters is the interaction.

The business school students appear to be collaborating, but in fact they are engaged in a process psychologists call status management. They are figuring out where they fit into the larger picture: Who is in charge? Is it okay to criticize someone’s idea? What are the rules here? Their interactions appear smooth, but their underlying behavior is riddled with inefficiency, hesitation, and subtle competition. Instead of focusing on the task, they are navigating their uncertainty about one another. They spend so much time managing status that they fail to grasp the essence of the problem (the marshmallow is relatively heavy, and the spaghetti is hard to secure). As a result, their first efforts often collapse, and they run out of time.

The actions of the kindergartners appear disorganized on the surface. But when you view them as a single entity, their behavior is efficient and effective. They are not competing for status. They stand shoulder to shoulder and work energetically together. They move quickly, spotting problems and offering help. They experiment, take risks, and notice outcomes, which guides them toward effective solutions.

The kindergartners succeed not because they are smarter but because they work together in a smarter way. They are tapping into a simple and powerful method in which a group of ordinary people can create a performance far beyond the sum of their parts.

This book is the story of how that method works.

Group culture is one of the most powerful forces on the planet. We sense its presence inside successful businesses, championship teams, and thriving families, and we sense when it’s absent or toxic. We can measure its impact on the bottom line. (A strong culture increases net income 756 percent over eleven years, according to a Harvard study of more than two hundred companies.) Yet the inner workings of culture remain mysterious. We all want strong culture in our organizations, communities, and families. We all know that it works. We just don’t know quite how it works.

The reason may be based in the way we think about culture. We tend to think about it as a group trait, like DNA. Strong, well-established cultures like those of Google, Disney, and the Navy SEALs feel so singular and distinctive that they seem fixed, somehow predestined. In this way of thinking, culture is a possession determined by fate. Some groups have the gift of strong culture; others don’t.

This book takes a different approach. I spent the last four years visiting and researching eight of the world’s most successful groups, including a special-ops military unit, an inner-city school, a professional basketball team, a movie studio, a comedy troupe, a gang of jewel thieves, and others. ^*2 I found that their cultures are created by a specific set of skills. These skills, which tap into the power of our social brains to create interactions exactly like the ones used by the kindergartners building the spaghetti tower, form the structure of this book. Skill 1—Build Safety—explores how signals of connection generate bonds of belonging and identity. Skill 2—Share Vulnerability—explains how habits of mutual risk drive trusting cooperation. Skill 3—Establish Purpose — tells how narratives create shared goals and values. The three skills work together from the bottom up, first building group connection and then channeling it into action. Each part of the book is structured like a tour: We’ll first explore how each skill works, and then we’ll go into the field to spend time with groups and leaders who use these methods every day. Each part will end with a collection of concrete suggestions on applying these skills to your group.

In the following pages, we’ll spend time inside some of the planet’s top-performing cultures and see what makes them tick. We’ll take a look inside the machinery of the brain and see how trust and belonging are built. Along the way, we’ll see that being smart is overrated, that showing fallibility is crucial, and that being nice is not nearly as important as you might think. Above all, we’ll see how leaders of high-performing cultures navigate the challenges of achieving excellence in a fast-changing world. While successful culture can look and feel like magic, the truth is that it’s not. Culture is a set of living relationships working toward a shared goal . It’s not something you are. It’s something you do.