During engineering, you must always train your mind to expect the unexpected. Many of you might be slightly irritated by when the teacher teaches how to solve a problem using a particular formula during the semester and asks for the proof during the exam. This behavior might be termed as unprofessional only when the teacher puts on such a question for failing students. Many excellent teachers give the concept well and then expect you to think out of the box during the exam. This is by far the best approach a teacher can take to teach engineering students well.