"Books on horse racing subjects have never done well, and I am told that publishers had come to think of them as the literary version of box office poison"

This quote by Laura Hillenbrand recommends that books about horse racing have actually not achieved success in the past, and that publishers have concerned view them as a monetary risk. This could be due to the reality that horse racing is a niche topic, and therefore the potential audience for such books is limited. It could likewise be due to the fact that horse racing is a busy and ever-changing sport, indicating that books about it can quickly become out-of-date. This quote implies that publishers watch out for investing in books about horse racing, as they are unlikely to be profitable. It is a suggestion that the publishing industry is a service, which publishers should bear in mind the financial dangers connected with any job.