The book made more than 100k as it's still selling pretty well. In fact, the sales have increased over time, even if the book is now 5 years old.

I keep on updating it and will release a second edition soon.

The marketing effort is not just for the book. It also helps me sell:

- video courses

- on-site training

- online training and workshops

- find consulting opportunities

- subscription licenses for a software product I created, Hypersistence Optimizer, https://vladmihalcea.com/hypersistence-optimizer/