losing focus and taking breaks, or being distracted by other things

Yeah, pretty much.

I guess my study technique merits description. For one thing, I've never had luck forcing myself to read something: if I don't want to, I don't. If I really need to learn something that sounds boring, I spend my efforts convincing myself that it's interesting (or finding an alternative method of learning it) rather than forcing myself to read. I don't seem to absorb information well when I force it upon myself. In part, the problem was that I found my impulses vetoing model theory more frequently than they vetoed other subjects in the past.

Also, there's this phenomenon (that I've never tried to articulate before) where when I first glimpse a surprising / difficult concept that looks like it's going to take some time to untangle / conflict with my existing model, I sort of... eject. Ideally, I then stare off into space / scribble on my whiteboard / meditate, as necessary. Realistically, I often end up reading fiction / dealing with email for a time before I can convince myself to attack the issue head-on.

I found that with model theory, I ended up spending more time in the "realistic" branch than usual.

Note that there are many confounding factors here; this could be related to enjoying the fiction I was reading more than usual / having more email than usual / having more "woah" moments than usual, etc. -- as I said, I don't have sufficient data to draw conclusions. Right now, I can only note that of the hours I allotted, I managed to spend less than half actually reading the damn book (which is less than usual).