Have you ever been part of a group project where one person seemed to do most of the work while everyone else quietly disappeared? Psychologists have a name for this surprisingly common behavior: social loafing.

The phenomenon was first explored by French engineer Max Ringelmann, who found that people pulling a rope together did not produce as much force as they could individually. Later research showed that the drop in effort was not simply caused by poor coordination. People can actually become less motivated when their individual contribution is harder to see.

One major reason is accountability. When no one can tell exactly who contributed what, it becomes easier to assume that someone else will pick up the slack. This is sometimes called the free-rider effect. There is also a related “sucker effect,” where hardworking people reduce their own effort because they believe others are taking advantage of them.

The size of a group can make the problem worse. As more people join a team, each individual may feel that their contribution matters less. If the task also seems unimportant, repetitive or unrewarding, motivation can fall even further.

But social loafing isn’t inevitable. Research has found that people tend to work harder when their individual contributions are identifiable, their responsibilities are clearly defined and the outcome actually matters to them. Smaller groups can also make it easier for everyone to see how their effort affects the final result.

There is another important factor: team loyalty. When people feel connected to their group and care about its success, they are less likely to sit back and let others carry the workload. Clear goals and meaningful responsibilities can also help prevent resentment from building among the people who consistently do more.

Interestingly, newer research suggests that taking a little less effort in certain group situations isn’t always harmful. Brief periods of reduced effort may sometimes help people conserve energy for more demanding tasks. The problem is when social loafing becomes a pattern that leaves a few people doing most of the work.

So the next time a group project feels strangely unbalanced, it may not simply be a case of one person being lazy. Group size, accountability, motivation and the way responsibilities are divided can all influence how much effort people put in. Sometimes, changing the structure of the group can change the behavior too.