In my undergrad institution biology majors took organic chemistry in our first year, and it was frequently referred to (by students) as the “weed out” course. Because it is rare to have a freshman organic chem course, our professor had written the book for the class. Whenever I, or anyone else, asked him a question about the material he would respond with “Look it up in the book” or some variant, suggesting that he could not explain it any better than what he had written. Of course this was a problem for me, because I would often have trouble understanding descriptions in the text, and wanted an alternative explanation, which it seemed he was unable to provide. I eventually lost the initial interest I had in the subject and wound up doing only what I needed to do to move on for my major.
Really, all that was needed for the professor to prevent this sort of demotivation was for him to be willing to be flexible. If he had understood that some students need different examples or explanations or that there are different ways to learn it would have been a better situation for everyone.