It is a skill to understand when to stop reading a book and switch to another one. Not finishing a book is not a sign of failure, rather it is a sign that you value your time even more. Reading non-fiction books in a serial way, i.e. one book after another is also quite inefficient. Reading a few books and jumping between them helps keep the interest level high. However, there might be advantages of sticking with a book in the case of fiction, especially when the story draws you into a whole another world and you develop a connection with the plot and the characters.