I heard this from a friend “Common sense is not a common sense.” It doesn’t matter from where he heard it or read it, it made my life easier. People don’t react to the same action the same way everyone else does. For example, you expect people to be quite in libraries and movie theaters. You may even go beyond this by believing that it is common sense for people to be quite in these places. Yet, you still see and hear people answering their phones in libraries and movie theaters.
As a graduate teaching assistant I hold weekly office hours. Some of the assignments the instructor gives to the students are due in two or three weeks. When a student comes in the last week of the homework submission I expect the student to at least have started with the project or read the material related from the text book. Yet, because common sense is not a common sense some students wants to finish three weeks worth of work in one office hour.
Another thing I heard is from a program I watched on the TV. “It is not what you know it is what you can prove.” Unlike many societies outside the US were the higher authority has the final word, here in the US he needs to prove what he knows. For example, a teacher can’t claim that his student cheated without a proof. In many other places it is the teacher’s word against the student’s word.