I have yet to sell a book, but I've finished three manuscripts and am almost 50,000 words into a fourth. When I'm in the zone and in drafting mode, I can turn out 80 pages or more a month despite working full time, having a 3-year-old child, and only being able to squeeze an hour or so per day out of the calendar to write.
If it sounds like I'm bragging, I kind of am. This is what I want to do, more than anything. (Well, more than anything I want to start SELLING those manuscripts, but you know what I mean.) So I've fought pitched battles with my own laziness, procrastination, and fear of both success and failure and trained myself to sit down, day in and day out, whether I'm feeling all creative and inspired or not, and put words on the page. And there are few tougher adversaries than laziness, procrastination, and fear. Steven Pressfield labels them Resistance, and his book, The War of Art (2003), is about defeating it.
For the most part, I found the book an inspiring reminder of lessons already learned. I like his focus on professionalism, i.e. doing the work whether you're in the mood or not. Wait for the Muse, and she'll ignore you. Start writing without the Muse, and she'll eventually come to bless you. Pressfield quotes Somerset Maugham: "I write only when inspiration strikes. Fortunately it strikes every morning at nine o'clock sharp." I heard the same basic idea from Bernard Cornwell at a writers' conference, and it's stayed with me. He says there's no such thing as writer's block, and the day a nurse can call her hospital and say she can't come in to work because she has nurse's block and have that accepted as a valid excuse is the day we have a right to put on diva airs and not write simply because we're stuck or aren't in the mood.
Anyway, I'm with Pressfield when he talks about overcoming Resistance and writing like a pro even when you're not getting paid for your work yet. But he loses me when he starts getting all visionary and mystic about the Source of creativity, and how the ideas are Out There and we're just the channels. Um, no. Way too New Age and woo-woo for me. I get my share of blinding epiphanies and "aha!" moments, but it's my own brain that's doing it. I can get plenty of joy and even sense of the numinous out of being a storyteller, another link in a long chain going back to the bards of old and even to grandmothers and grandfathers around the fires in Paleolithic caves, without believing I'm nothing more than a channel for the muse.