Invariably, groups that had the bad apple would perform worse. And this despite the fact that were people in some groups that were very talented, very smart, very likeable. Felps found that the bad apple’s behavior had a profound effect — groups with bad apples performed 30 to 40 percent worse than other groups. On teams with the bad apple, people would argue and fight, they didn’t share relevant information, they communicated less.

Even worse, other team members began to take on the bad apple’s characteristics. When the bad apple was a jerk, other team members would begin acting like a jerk. When he was a slacker, they began to slack, too. And they wouldn’t act this way just in response to the bad apple. They’d act this way to each other, in sort of a spillover effect.