There are a million things that we do in the classroom every day that make or break a lesson. Just as there are good ways to give a lecture, there is an assortment of ways to encourage discussion, starting with how we look and act in front of our students and certainly the kinds of questions we ask. The way that we receive that information and incorporate it into the final discussion contributes to the final portrait that you and your class have painted. Is it a piece of art or is it trash? Yes, 20% versus 80% seems about right.