Opportunity Cost

Here is an interesting result. A shameful result according to Marginal Revolution?
But is it surprising? When I was in graduate school my girl friend and classmate got upset at our micro teacher because I got a higher score on the midterm exam then her. As an undergrad she was a math major and she was helping me with the math. I confess I am at best average when it comes to math. She was mad because my math on the exam was all wrong and yet I scored a higher grade then her. She wanted to know why?
Dr. S. (the teacher I try to copy when I teach micro) told her "Mike screwed up in the mechanics of the math but his economic reasoning is sound." He continued after thinking for a moment "Your math is flawless and the proof you provided is wonderful but how does it work in Economics."
She could not answer him.
In case you are wondering the question was about cost. She had calculated all the explicit costs accurately but had overlooked what she angrily called "B**L S*** Cost" !
I do not find this surprising at all. If you want the finance version of this read Financial Rounds.