It looks like you switched to using an affiliate tag to promote that book. Can you share with us what the earnings are from a typical link on HN?
https://www.google.com/search?q=site%3Anews.ycombinator.com+...
https://www.google.com/search?q=site%3Anews.ycombinator.com+...
I'm not sure if we should feel betrayed by this sort of behavior, if you're going to post a link to a book anyway.