Most packaged goods companies would kill to be the only product on the shelf, to own the category in a given store. Yet, not only do authors get along, they spend time and energy talking-up each other's books.
Can you imagine Bill Gates giving a generous review of Apple's new operating system (OS) or Tim Cook writing a positive blurb about the Samsung Galaxy S5? And yet, the authors do it all the time! To read more about this unique perspective, check out this article written by Seth Godin.