When you stay put in one area, you will not improve. Students of teachers who upgrade their knowledge will thus find themselves better off relatively in terms of knowledge.

It's a matter of perspective. Your teacher had far more knowledge than you did at a young age. As you gained knowledge you became a peer to your teacher and possibly surpassed the teacher in knowledge. Just like returning to a place in your past that seemed huge to you and it's amazing just how small it looks when you go back.

1) No problem, as long as it is not those from whom you want to learn. ------ ADDED (Explanation) ------ 2) We overcome our teachers: I certainly agree, after some years, I recognize that my former teachers are just people like myself, with their qualities and their flaws. And as I had many other teachers in the meantime, I have learned a lot, and know many things than they don't know. And I realize that they sometimes are not so clever as I thought at that time. 3) The choice of one's teachers: When I was a child, I had to take the teachers what I got (at school). It was more a matter of luck then, or which teachers my parents could afford for me. Later in life I can learn further from all the people that I meet. Those are also my teachers in a more general sense. And in this moment, I have much more power on choosing whom I wish to listen to and whom I prefer to ignore. In this moment, I choose those teachers from whom I assume that they can teach me something, or those who seem to be particularly clever. 4) Anyway, I am aware of the luck that I had to have some of my teachers, or read some particular books. Sometimes, we are just dwarfs standing on the shoulders of giants... http://en.wikipedia.org/wiki/Standing_on_the_shoulders_of_giants