If the student is paying attention to you and they're not getting it, it's your fault. That's the difference between a good teacher and not. Teaching isn't easy. You're the only one who understands it. You have to understand your subject from all directions and be able to explain it in novel ways. The only way the knowledge is transferred is if you figure out how make it obvious to them. After that point is when study comes in.
Every student is not Pythagoras. We all remember him. We all consider his theorem to be easy and simple now, but how many would have figured it out without someone explaining it in an obvious way? I had teachers who made everything obvious and I've had teachers who were useless and had to teach myself. I try to be the former.
