Yeah, you read that right — observing a demo is worse than having no demo at all!  The problem is that you see a demo, and remember it in terms of your misconceptions.  A week later, you think the demo showed you what you already believed.  On some of the wrong answers that students gave in Mazur’s study, they actually said “as shown in the demo.”  The demo showed the opposite!  The students literally remember it wrong. People remember models, not facts, said Mazur.  By recording a prediction, you force yourself to remember when you guessed wrong.