There is a subtle difference between good teacher and a teacher who seems to be doing things correct, but still the students feel uncomfortable about what he/she taught. Both of them can tell you the correct things and also explain why they are correct. Difference comes in their treatment of what you are thinking. The good teacher is able to understand exactly what you are thinking and can tell you why you are wrong, if what you thought was wrong; or can tell you how both of you can be correct at the same time, if what you thought was also correct. A teacher in the other category can not do that. And that makes quite some bit of difference.