When I was young (think middle school) I would read 3-4 books at a time. Not because I like the challenge but because I got bored or the book had larger or more complex words that I was not familiar with. So I would take a break from it and try another.
Nowadays I treat audiobooks the same as I did when I was young. I also read book I really want to read one at a time these days. I have liked savoring the story a bit more or reflecting on what I read a bit more than just trying to read the book, this has allowed me to get through books that when I was younger I would avoided for the slow pace.
Now if I truly detest a book for any number of reasons I will drop it. It doesn’t mean I won’t go back to finish it, but the best example is Wheel of time by Robert Jordan. I got to book 7 and I finally had, had enough. I just could not deal with the amount of groups he would switch between to tell his stories. The books and story aren’t bad, I just go tired of dealing with it.