When I read something with the sole goal of understanding the main points, I end up in a fight with the author. When I don't understand what he's saying, I have to slow down my pace. This is annoying, and it means that I'm losing. When I'm basically understanding each of his points, I read at a normal pace. We're tied. But when I already grasp his current point and my internal dialogue is mocking him to get to the next one, then I speed up. That's the fun part, and it means that I'm winning.
When I re-read my old stuff I often end up fighting with myself. Sometimes, it gets ugly.