Writing a book is a slow process, much slower than I first expected -- there are always small things to do, such as correcting Figure numberings, checking spelling, or fixing poor wordings and explanations. The truth, however is that most writers enjoy this process. Perhaps 14 hours at a stretch is a bit too much -- and I will admit that I would prefer less onerous hours (a publisher's deadline does tend to focus one's efforts) -- but I do enjoy the process, and feel great satisfaction at producing informative, readable, and accurate prose.