When I went to college I had one professor who actually had owned a few businesses, had traded on the floor of the CME and had about 50 sets of professional initials after his name, had every license the trading world has to offer, Had several published books on securities trading, had a PHd from Columbia and would not accept any answer that wasn't hard thought.
He was a thorn in the side of the liberals. 80% of the students hated him because he was HARD and did not accept answers that were not well thought out. If you talked in his class he would throw you out, and he would randomly pick people to answer questions from the work assignment 2 days earlier. You really had to be on top of your shit because he failed people left and right, got a lot of flack from the Administration for failing students too. He said it was his duty to send people out in the world with an education, not hold their hand until graduation.