"Making the course harder than it has to be" relates mostly to how the content is taught in class.

This can be due to a number of things on a course-wide scale or simply down to how individual lectures or topics are lain out.

Overall this may be due to poor perspective on the part of the professor. He/she never really overviewed the course content **from the viewpoint of an incoming student who has all prerequisite courses successfully completed** and then structured the lectures accordingly. 

On a single lecture basis, it usually means a professor not arranging their lecture in a pedagogically appropriate way, i.e. building on the concepts already known to students and guiding them rationally and sensibly towards their next concept plateau.

But occasionally it also means the **professor's delivery of the lecture**  leaves the students with misunderstandings on the concepts, their relative importance or offers ideas that run counter to the student's intuition or common sense. Here there are different causes, including:

1. The professor may have a natural insight into this concept and assume everyone else also has - though of course they don't.

2. The professor himself/herself has a poor grasp of the concept and is just trying to bang home some (often poor) textbook version of it with a hammer and tongs.

3. The professor's pacing, tone and volume is not proportionate to the importance or complexity of the current content.

4. The professor has very poor vocal projection.

5. The professor chooses an unorthodox (e.g. interactive) approach to a topic that doesn't lend itself to such teaching.

I would say that every professor has one or two of these shortcomings when they start out in their career. To my knowledge, no university **insists** on professors having to take a teaching course prior to starting lecturing themselves. Yet most learn from their mistakes and the advice of senior colleagues. Many take student observations seriously (after an initial sulk) and adapt their approaches accordingly. But some will maddeningly carry on regardless and neither colleagues nor university management will intervene.

Just one final point on "making courses harder". 

The best way to teach something is the clearest way from the point of view of someone not yet familiar with it. Sometimes students (and adults no less) in the euphoria of achievement can forget just how lost they were before they "got" the concept. They then have the confidence to look at the concept in another way and find they can arrive at an understanding - actually quicker, providing you already know of course - by looking at it like that. Then they try explaining it another student in "their own" way - only to thoroughly confuse that student.

Sometimes it's well to remember that the first working out of something is necessarily elaborate rather than elegant. Lessons learned with a bit of work and worry are seldom forgotten - unlike the tricks of elegance.