Final answer:
The irrational belief from the given options is that the book's poor sales are due to an industry bias. Rational responses involve proactive reflections on improvement, while attributing outcomes solely to luck or external biases is considered irrational.
Step-by-step explanation:
The best example of an irrational belief when a book does not sell well is option b, "My book didn't sell well because the publishing industry is biased." This belief falls into the category of attributing outcomes to external factors beyond one's control, which often does not account for all the complexities involved in the situation. On the other hand, options a, "I need to improve my marketing strategy for the next book," and d, "I should have hired a better editor for my book," are rational responses that involve reflecting on possible improvements. Option c, "The success of my book is entirely dependent on luck," could be seen as irrational because it ignores the many factors that can influence a book's success and attributes it solely to chance. The businessman's comfort in believing hard work is its own reward represents a belief about one's own outcomes being within one's control.