.. there seems to be a bittersweet joy in the end of semester grading.
You know you are almost done. You know that the little twerps won't be in your pile next semester -- unless they choose to be... and then they know what they are getting into.
Having a short list of things to grade is wonderful because it is finite.
Philosophical research can go on forever. Another revision could make it better written, another book read could make it smarter and another deep thought makes it, well... deeper.
Grading is just a stack of papers and when they are graded, they go away.
True, it is sometimes sad that they didn't learn what we are trying to teach them -- but, I always hold out some hope that they learned something else....