In the early 1970s, a cohort of Stanford students participated in an unforgettable experiment. They were shown a collection of suicide notes-some real, some fake-and asked to tell which were real. The task was difficult, but most students managed to do reasonably well.

Then the twist came. The researchers told half the group that they had done exceptionally well. The others were told they had failed miserably. But here's the catch: none of it was true. The feedback was fabricated.

After revealing the deception, the researchers asked the students how they thought they had actually performed. Those told they had done well still believed they were naturally good at the task.

Those told they had failed assumed they must have missed something obvious. The fake feedback had taken root, and it refused to let go-even after the truth had been laid bare.