"Then, you get your Master's, and you realize you don't know anything."
"Then you get your Doctorate, and you find out that nobody knows anything."
Took me about 3 months to figure out why the java class I was taking was so screwed up. The professor had never seen Object Oriented Programming (or Java) before. He was staying one chapter ahead of the class and picking assignments that required his domain expertise to complete.
As annoying as it was to find out, I still learned a useful bit of Java. Took me years (and learning ruby) to actually grok objects correctly.
Not grasping OOP makes using Java a tad difficult.
They once sent out a sectionwide e-mail announcing a new mobile app development course. One of my coworkers responded with a "thanks, I need that badly!" to which, amusingly, he was told that he was to be the teacher!.
Edit: I have found that "The best way to learn is to teach" (attributed to Frank Oppenheimer) is quite true.