Minjin said:
Because you don't understand the concepts. This isn't a slight to you but to your professor. I've seen way too many people teach towards problems, how to calculate this or that, but not WHY you do this or that.
Yes, and it's poor planning/presentation by the professor when instances and problems pop up that have variables (not in the strict sense) that were not in the examples or taught. Some books are decent at explaining problems, and some are absolute crap. Teachers are the same way, and probably the number one problem that we (both) have is we assume that people know things or that they know to do a certain thing. It's so easy to fall into the trap of, "well I know this subject, and it's easy, and I should only have to explain this, and the students should understand it". Or, "why doesn't this person understand this? It's so simple to me (because I've been doing it all my life)".
The amount of knowledge, repetition, guidance, and understanding that it takes to be able to correlate knowledge/learning (being able to correlate is the highest level of learning) is very immense, and I think that many teachers vastly underestimate this.
I don't assign much homework in my educational job (due to what I teach), but if I'm having a very good day and I'm on top of my game, I can lead a student to correlate subjects through carefully worded questions and guidance. Sometimes though, it will not work, and no amount of effort on my part will instantly bring the intended results. Now, send a student home with homework and have them do this (try to correlate) on their own. It's often a lot to ask. "Understanding" is a level that is below correlation, and as the original poster said, it's often not difficult to understand what is going on in a specific example that is given when it's described. Correlation involves applying the same concept to problems outside of what was originally learned. With superior knowledge, experience (application) and practice, it's all too easy to forget what it's like to learn something, and to apply it to (at least seemingly) different situations.