It's getting easier for me.
There are some books (non-fiction books in particular, but some fiction as well) that made me uncomfortable or I that I just couldn't get into, but that I felt were important enough to keep reading, so I've pressed on though I wanted to stop.
With unimportant books, though, I have gotten past my "sunk cost fallacy" of having to finish them because I don't want my previous investment to go to waste.
I've finally come to understand that my current and future time have value, while my past time and money have none. Whether I read the book or not, the time and money I've already put into it are gone, and I can never get them back. I'm not going to chase that bad investment by spending my valuable current time on it. If I can get better utility out of that time by doing anything else, I will.