Books have a soul; if you can't get into a book, it's usually because it doesn't resonate with you.
Even the same author can write different books with different souls.
I can finish *One Hundred Years of Solitude* in one go and be deeply moved, but I've only read a third of *Chronicle of a Death Foretold* by Gabriel García Márquez and still haven't finished it; I can read *Siddhartha* fluently, but I struggled with Hesse's *Steppenwolf*.
Finding a book that resonates with your soul is a stroke of luck.