Suppose that, while teaching a class some engaging topic, I keep a secret from the class and only reveal it at the end of the term. This secret provides a sudden realization to the students that they can take into their next year — A real ‘Aha! moment’. I only ask them that they do not reveal the secret to any classes that haven’t taken the course yet so that they can have the same experience. This may work for a while, but inevitably one student, through malice or ignorance, will reveal the secret to someone they shouldn’t have. This then spreads throughout the whole student body until the experience for all future classes is ruined.