Most products, including books, are combinations of tangible and intangible elements. People do not buy the tangible features of a book, i.e., the paper and ink that create it. They buy the intangible benefits they receive from reading fiction: a vicarious feeling of fantasy, romance, adventure or mystery. And when purchasing nonfiction, they are buying information, motivation and help.
As an independent publisher, you will become more successful at marketing when you stop selling your books and begin selling what your books do for the people who read them. That is the difference between marketing a feature, an advantage and a benefit. A feature is an attribute of your book. It could be its size, binding, title or number of pages. An advantage describes the purpose or function of a feature, and a benefit is the value the reader receives in exchange for purchasing your book. People buy value, not generic books.