When a book is repeatedly pulled by the headcap (the weak upper portion of the spine) it will eventually fail, tear, and need repair. Removing a book from the shelf as shown below can damage the headcap.
There are many examples such as this one (below) in the collection that show the result of removing a book from the shelf by pulling from the top of the spine material.
Books should rest vertically on the shelf so they are supported by other books or a bookend. Sometimes when you remove books to look at or borrow, this can happen.