Staying focused on endurance runs

I need some advice from the serious athletes out there.

This week I cross a line: my long run next Saturday is 15 miles, which will take me more than 2½ hours to complete. I’ve noticed that line is more than just a test of endurance—it’s also a test of focus.

Simply: you have trouble staying focused for a movie that’s longer than 2½ hours, right? I’m having the same trouble with my long runs.

These days I run to audiobooks instead of music. I find that the audiobooks do a far better job of distracting me from the mechanics of running. It messes with my head when I think about the mechanics, tripping me up. If I lose focus, I get into this sort of wedged loop in my head where I can’t think about anything other than the mechanics. But even the most interesting audiobook, like an interesting film, is going to lose me at that 2½-hour mark.

I don’t think it’s an energy or blood sugar thing. I’ve been finishing the long runs with energy left—at least, not so dead that I want to vomit or pass out. But maybe it is? I don’t know.

Anyone have any ideas?