This is probably not the lean agile answer you're looking for. I was approached by a publisher who had seen some of my writing elsewhere. I pitched a book idea

This is probably not the lean agile answer you're looking for. I was approached by a publisher who had seen some of my writing elsewhere. I pitched a book idea at them that I wanted to write; they liked the idea but not the exact content. I ended up rethinking a few things, and pitching a similar but different idea to them, which they loved. I got a contract and started writing, and honestly the editing they gave me was unbelievable. I thought my writing was on the 'ok' end of decent, but they gave me some really valuable insights. The quality of the book was much better for going through their process. (It's a book in the Smashing Magazine series, some of which isn't technically amazing, but there are some great books in that series and I like to think my book is good ;) If I was going to write another book, I'd possibly think about doing it myself, but in all honesty I'd probably go the traditional publisher route again.