Like relationships, sometimes book success is dependent upon hitting the mood of the readers at just that right moment. I get asked all of the time how to create a best-selling book. I don't have a formula. I've come to the point where I simply admit it's a crapshoot, do you want to play or not? Many factors can influence or derail a book's success. The mood of the readers is one of them. Perhaps you've written an amazing action-adventure but everyone is reading fantasy and action-adventure literally overnight became passé. You're about to release your book and its publicity and potential success is suddenly eclipsed by the release of a mega-seller that everyone wants to buy, and your book has absolutely no relationship to that subject matter. Maybe the cover is off-beat somehow. We had one book where it's about vacations, and everyone thought it looked like summer and it was released for the Christmas holiday vacation season. This misconstrued thought about the "light" cover pushed people away from it. So, timing and perception can affect success.
When I get asked the all-important question, "How do I make my book a best-seller," I tell authors these many factors have an influence. When an author asks how to theme a book to make it more marketable, I explain the impact of these factors, and we discuss it. And none of it matters whether your book is non-fiction or fiction; all of these issues will still come into focus. Frankly, you just never know what people will want to read. I think I generally know, but I have been wrong not only in what ended up succeeding but also in what failed. And believe it or not, content is not always king. Some of the most well-written books have failed. Some of the marginally written books have succeeded. And when I share this with authors who truly buy into the thought that content trumps all else, they don't believe me. The falsely believe their content is superior, and therefore, will be hugely successful. While I am not suggesting you debase your content; what I am saying is that sometimes it just doesn't make a difference. So as it is with many things, what will be will be. My main goal is simple: just enjoy the pleasure of the ride of writing it. If it succeeds, celebrate. If it goes OK ... well, I enjoyed the experience.