My student's sentence: Getting married before graduating from university is not a shrewd and sensible choice.
I've corrected their choice of coordinating conjunction "and" to "or" [i.e. Getting married before graduating from university is not a shrewd or sensible choice.] but I'm having trouble explaining my instinctual decision. I wonder if it has anything to do with the word "not" and how it might be drawn parallel in usage to the correlative conjunctions "neither... nor"? Or is it because shrewd and sensible are conditions that don't have to be simultaneously applied to the situation?
I would appreciate it if someone could shed some light on this question as I am properly discombobulated!