Social psychologists Henri Tajfel and John Turner have found in their research that we tend to associate our identity and self-esteem with group membership.

Tajfel and Turner write in their paper The Social Identity of Intergroup Behavior that there are two effects of this tendency:

1. In-group favoritism: we favor those in our group. 

2. Out-group bias: we’re biased against those outside our group.

Their research, which has been corroborated by other studies, helps explain the durable attachments many of us have to various groups: from ethnicities and religions, to companies and sports teams.

You might expect this. 

In one experiment, they split strangers into groups using a coin toss to determine group membership.

Tafjel and Turner told one group that they were together because they liked one type of art.

As a result, the members of that group saw their fellow members as more agreeable than members of the others groups. 

Even though they were strangers selected at random, and weren’t art connoisseurs.

In his book The Art of Thinking Clearly, author and entrepreneur Rolf Dobelli writes that if you’re like most people, you’ve had the experience of biting your tongue in a meeting: “You sit there, say nothing, and nod along to proposals.”

You don’t want to be the naysayer. Besides, you might not be sure exactly why you disagree, whereas the others are unanimous. 

As Dobelli points out, when groupthink leads to negative outcomes, it’s usually because everyone in the group shares the following three illusions: 

1. A belief in invincibility: This sounds like, “If both our leader and the group are confident that the plan will work, then luck will be on our side.”

2. Perceived unanimity: No one wants to destroy team unity. If others are of the same opinion, then any dissenting views must be wrong.

3. Fear of exclusion: In our evolutionary past, expressing reservations and being excluded from the group meant death. So each person has a strong urge to remain in the group’s favor.

Dobelli cites the defunct airline Swissair as an example of groupthink gone awry in the business world. A team of highly-paid consultants rallied around the former CEO and, bolstered by the euphoria of past successes, they developed a high-risk expansion strategy. The team built up such a strong consensus that even rational reservations were suppressed, which led to the company’s collapse.

To guard against groupthink, Dobelli suggests that whenever you find yourself in a unanimous group, you must question tacit assumptions and speak your mind – even if your team doesn’t like it. 

And if you’re the leader of a group, appoint someone to act as devil’s advocate: “She will not be the most popular member of the team, but she might be the most important.”

Author and researcher Josh Kaufman writes in his book The Personal MBA that over time, you become more like the people you spend time with, and less like the people in other groups.

For Kaufman, this observation is explained by two tendencies: convergence and divergence. 

Convergence is the tendency for group members to become more alike over time.

It also explains how groups tend to police their members’ behavior. 

As Kaufman puts it, a group’s norms can act like gravity: “if they are violated, others will exert an influence on the rebel to bring them back in line.”

For example, say you work at a company that has a workaholic culture. If it’s normal to start work at 6am and finish at 10pm, then it can be difficult to work shorter hours. Violating the norms is a signal to the other members that you don’t belong in the group. 

Divergence is the tendency for groups to become less like other groups over time. 

Group behavior often evolves to distinguish members of one group from other groups. This means that a group’s norms will change over time to ensure that the group can’t be confused with another group or imitator. 

For example, divergence explains why fashions among the socialite class in New York City change so quickly and dramatically. 

In such a social circle, dress is a way to signal your wealth or status. But when the latest fashions start appearing in a store like Target allowing others to imitate a given look, that social circle will change its fashions to compensate.

Kaufman suggests that you can use convergence and divergence to your advantage. 

If you want to become less shy and more outgoing, spending more time with social people will start to influence your behavior. On the other hand, if you find yourself spending time with people whose behaviors aren’t serving you, break away. 

“The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is a hard business. If you try it, you’ll be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.”

- Writer Rudyard Kipling in a 1935 interview