The relationship between a teacher and student is an interpersonal relationship. It's like a friendship. The effect of a good teacher, as I see it, is not that

The relationship between a teacher and student is an interpersonal relationship. It's like a friendship. The effect of a good teacher, as I see it, is not that you get more knowledgeable about a field. You can do that from a book or the internet. It's to motivate you, to make you excited about a field, because they showed you what they thought was exciting about it and you agreed. Bad teachers can make you hate a particular field for the rest of your life.