I'm discussing the importance of niche validation in book publishing.

I'm sharing my experience of finding a niche, improving a book to compete with an existing one, and investing in advertising to make it successful, resulting in $18,000 in earnings.

I also emphasize the strategy of creating complementary books within the same niche and the value of organic sales before running ads.

Lastly, I mention the significance of having most of my top-earning books within a single niche.