In the 1940s, more than 7000 books were published in the United States, of which only more than 10 became the best-selling books  A publisher in New York found that the best-selling books of the year were related to three subjects, one related to President Lincoln, one related to doctors, and the other related to dogs He thought that if these three kinds of content were combined, they would be the best-selling books
So he planned to publish the Pet Dog of the President of the United States and Physicians, which turned out to be a particularly poor seller
Ignoring other possible reasons.