My secret was I didn't write more than 5% of the book. 95% came from discussion posts written over the years on one of my website forums.
I still get orders.. I'm still in the top 500 small business / real estate books in canada. This was written in the 2012 and lives on.
I would encourage everyone to publish at least one book. But don't actually write it yourself that's insane amount of work for the expected return.
[1] https://www.amazon.ca/Ontario-Sale-Property-Buyers-Guide-ebo...