When Johnny’s history teacher suspected him of copying Mary’s test, he wasn’t ready to admit a thing. The teacher pointed out that their answers to questions about George Washington and Abraham Lincoln were identical. Johnny had an explanation ready: he had studied hard the night before. After all, two students getting the same facts right wasn’t necessarily proof of cheating. For a moment, his argument sounded reasonable enough. Then the teacher moved to the question that made his entire story fall apart.

The question asked who was president during the Louisiana Purchase. Mary, unable to supply the answer, had written, “I don’t know.” Johnny hadn’t named a president either. Instead, his response was, “Me neither.” Those two words did what the matching correct answers couldn’t: expose exactly where his inspiration had come from. He had tried to borrow Mary’s knowledge—and ended up borrowing her uncertainty a little too honestly.