It's rude to risk someone's academic standing by copying them.
Larry has a big exam coming up in school that is notoriously long.
Larry wants to complete the exam on time.
Larry does practice exams to make sure he is within the time limit.
Larry looks for a student that is ahead of him in the exam and writes what they write on the exam.
Larry completes the exam on time and the other students are not bothered.
Larry and the other student get in trouble with the Professor.