Okay. If you're looking for full disclosure from me, neither does my writing - it's more a self-supporting hobby to date. But unless I obtain a job in sales and marketing (which will only happen if the pod people get me - as neither sales nor marketing are among my core competencies) writing is my sole avenue for potentially paying the bills. Some day.
Is there call to track numbers, ever? Absolutely.
- You're self-pubbing
If you are pubbed by one of the big publishing houses, you aren't going to be able to accurately track sales numbers until royalty statements begin arriving. But when you're published by one of the big houses, sales benchmarks have a tendency to matter more than units sold. Did book x earn out? Did books 1 and 2 sell enough copies to justify a book 3? Then, when you're no longer concerned with those benchmarks (because the answers were all YES) the benchmarks involve hitting lists.
At the end of the day, though, the reason I don't stress book sale numbers is because once a book is released, nothing I do (beyond being a reasonably decent human being - social media, speaking, going to signings - you know - the normal stuff authors do) will make someone buy a book. Driving yourself crazy, fretting over something you ultimately can't effect unless you're herding people into the book store at gunpoint to buy - it just seems self-defeating. Write. Edit. Copy edit. Publish. Promote within reason and then RELEASE. Take a breath. Start the process over again.
Maybe it comes down to a question. What do you love? The writing? Or comparing your Amazon ranking against your nemesis's and feeling small because you either don't rank as high, or you do and your short-lived sense of triumph is punctured by the misery of wondering whether you'll be able to stay on top? If it's not the writing, there *are* easier ways to get your nemesis's goat. Not that I have deep, personal experience.