A fog that lifted

I am not sure what to call this, but it has now happened twice. I started reading a book and I find the language used quite difficult. To a point where I find myself backtracking multiple times. This is frustrating, so I stop reading the book. But when I come back, the language is demystified - like a fog that has lifted. This has now occurred with Hyperion and with Revelation Space. It’s an odd experience.