Most Difficult Job for a Teacher???

If one were to ask an instructor which is the most difficult part of his job...It would involve things like class control (especially for a new instructor), time management, preparation, mental effort and so on....

But I personally feel that the most difficult part of the job is evaluation, and when I am saying evaluation in mean not the physical aspect of checking and grading, but the mental aspect where you actually have to rank you students and say that one is better than the other. Maybe for some people the job might be easy, but for an average person this part is the one which would make him uncomfortable. This discomfort would increase with as the familiarity and time you have spent with the students increases, because then you have to be doubly sure that none of your biases are creeping in …. 

Maybe a quanty Prof might have an easier job evaluating  .....