Second, yes, maybe I was not clear, my advice relates to the average author on a simple straightforward method of write a book that reduces the odds of it not being of use of the audience it seeks.

Lastly, might be wrong, but it appears:

(A) at least on Amazon, your book appears to be rank in the top 20,000 of all books;

(B) you appear to have published a singular book;

(C) as you say, yourself, it does not make enough for someone to live in a major city;

(D) writing books is not your primary means of income;

—- to me, what I hearing does not conflict at all with my analysis and your example, to me is survivor bias: https://en.m.wikipedia.org/wiki/Survivorship_bias

——

Writing multiple best selling books year after year is VERY hard to do as a means of income. There are much easier ways to earn an income and share what you know. If someone wants to do that, awesome, though I do not have advice for doing that, nor do I know of anyone else that does; that would result in publishing 1+ successful books a year. My advice is just no nonsense take on being reducing odds of book being useful, which for the average author is much more of a challenge.