The most important message of the video can probably be described as
follows: do not move to more advanced topics before being sure that
less advanced topics have been learned by students, at least
partially. Call this the POP (Principle Of Prerequisites).
In my opinion, learning SHOULD and CAN BE pleasurable. How can this be
achieved? By rigorously applying POP. Unfortunately, students are
often deprived of the pleasure of learning by grade inflation.