Writing a book is a long, hard process. It's never-ending, too: As soon as you finish one, you really need to get started planning, outlining, and writing the next. But you also need to spend time selling and marketing. Very few writers, if any, are in it for the money. It's too much work with not enough return. Especially if you're an indie writer. Still, we try to sell our goods with the hope that one day we might support ourselves with our writing and therefore have more time to spend writing.
The biggest problem with selling: it takes a lot of time. Sure, you can release your book to the world and hope it gets traction on its own. I tried that for a while. For me, it didn't work. It wasn't until a combination of enrolling in KDP Select and implementing various engagements on Goodreads (advertising, giveaways) that my books started to get in front of people and start selling. But not only does the KDP Select rankings boost fade, Amazon also tweaked the algorithms so the whole process of going free just isn't as effective anymore. Goodreads is more of a slow, steady burn, not a bonfire. Slow and steady is a good long term strategy, but I like having a bonfire every once in a while, too.
Other marketing strategies include tweeting about your book like the world is about to end and getting others to re-tweet your tweets (how effective is this? This guy doesn't think it's very effective at all), letting every site possible know about a sale or free promotion you're running, paying for a sponsorship with Kindle Nation Daily (I've got one coming up in a couple of weeks) or other site, or hoping one of the mega-sites like Pixel of Ink will pick up your book whether it's on promotion or not. Selecting dates and coordinating all of this isn't a huge amount of effort, but when you're working a day job every hour counts. Typically when I schedule a promotion and advertising to go along with it I lose a day of writing (a day of writing for me is a couple of hours in the morning or evening before or after work). Add into the mix time spent engaging with readers (and other writers) on various forums and Goodreads, too.
The bottom line is that marketing is an ongoing process that requires time and effort that ultimately gets sucked out of the time and effort spent writing.
That's why I've decided to take a break from it all (the marketing, not the writing). Besides for an upcoming KND promo and my usual Goodreads self-serve ads, which run pretty much on auto-pilot, I'm stepping back and re-focusing on just writing. I'm about 40,000 words into the next book in The Alchemancer series. I got side-tracked a bit with a few changes in the outline. Ultimately those changes make the story much more concise and engaging, so time spent reworking that was well-spent, I think.
Hopefully if this works and I can resist the marketing temptation I should have this next book done in rough draft form within a couple of months. That's really my goal at this point: getting another book out there. I hope to have it complete by the end of the year.