When the lead singer at the concert asks you to scream as loud as you can, and then he asks again, going, “I can’t hear you! You can do better than that!” have you ever noticed that the second time is always louder? Why wasn’t everyone yelling at the top of their lungs the first time? Some really cool scientists actually tested this in 1979. (They) had people shout as loud as they could in a group and then alone, or vice-versa. Sure enough, the overall loudness of a small group of people was less than any one of them by themselves. You can even chart it on a graph. The more people you add, the less effort any one person does.
If you know you aren’t being judged as an individual, your instinct is to fade into the background. To prove this, psychologist Alan Ingram ruined tug-of-war forever. In 1974, he had people put on a blindfold and grab a rope. The rope was attached to a rather medieval-looking contraption that simulated the resistance of an opposing team. The subjects were told many other people were also holding the rope on their side, and he measured their efforts. Then, he told them they would be pulling alone, and again he measured. There were alone both times, but when they thought they were in a group, they pulled 18 percent less strenuously on average.
This behavior is more likely to show up when the task a hand is simple. With complex tasks, it is usually easy to tell who isn’t pulling their weight. Once you know your laziness can be seen, you try harder. You do this because of another behavior called evaluation apprehension, which is just a fancy way of saying you care more when you know you are being singled out. Your anxiety levels decrease when you know your effort will be pooled with others’. You relax. You coast.
David McRaney, You are Not so Smart