It is terribly unfortunate that incompetence and overconfidence are found in so many areas. Though I do not completely blame the individuals as there were far too many Professors at school that created doubt in students' minds as to what extent their education was required in order to do certain work. Some were excellent, of course, but others did not engender sufficient trust in the faculty as a whole (meaning, of course, most of the more temporary professors that passed through Hogwart' halls, though Professor Lupin was a refreshing exception).
When in doubt, a good aged Ogden's firewhiskey tends to cure the day's ills.