Don't feel disheartened by seeing unfinished books lying around in your house. And don't make the huge mistake of assuming that it's a problem to be rectified before you could buy new books.
Books that are unread on your bookshelf (or in the brought list in Amazon account) have two benefits.
You get to see how much you don't know.
And you also get the opportunity to read.
By having unread books, they make sure when you are bored and not in the mood to read the book. You can open up a fresh new book as per your mood.
For example, if you are feeling not that business mood to read another book on business, you can change your mind and read a book meditation.
I always read 10 books together on diverse subjects (history to sexuality), and there is never a day where I feel like I don't want to read any book at all.
That's why, next time when you are in a bookstore, don't shy away from buying books that you think you won't have time to read, even the presence of them lying on the sofa will make you crack open it.
You should be adding as less as friction to your reading habits as possible, and one way is to do this by building an anti library.