" In my experience, the books that tend to flop upon release are those where the author goes into a cave for a year to write it, then hands it off to the publisher for release. They hope for a hit that rarely comes. On the other hand, I have clients who blog extensively before publishing. They develop their book ideas based on the themes that they naturally gravitate toward but that also get the greatest response from readers. (One client sold a book proposal using a screenshot of Google queries to his site.) They test the ideas they’re writing about in the book on their blog and when they speak in front of groups. They ask readers what they’d like to see in the book. They judge topic ideas by how many comments a given post generates, by how many Facebook “shares” an article gets. They put potential title and cover ideas up online to test and receive feedback. They look to see what hot topics other influential bloggers are riding and find ways of addressing them in their book.* The latter achieves PMF; the former never does. One is growth hacking; the other, simply guessing. "
― Ryan Holiday , Growth Hacker Marketing: A Primer on the Future of PR, Marketing, and Advertising