People interact — constantly. But how does interaction affect our skills, our performance, our success? In the classroom, students listen to each other and may learn something new, but do they learn something true? When employees share knowledge, they may hear new ideas, but are these valid ideas? When you return from a conference, or a cocktail party, are your skills improved? Here we show that even if you return with fresh or exciting ideas, your skills — on average — have deteriorated. Interaction harmed your performance.