Final answer:
The best example of an irrational belief is option b) 'The readers are not interested in good content.'
Step-by-step explanation:
The best example of an irrational belief in this scenario is option b) 'The readers are not interested in good content.'
This belief is irrational because it assumes that the reason for the book's lack of success is solely attributed to the readers' disinterest in good content. It disregards other possible factors that may have contributed to the book's performance, such as marketing strategy or timing.
It is important to consider multiple factors and analyze the situation objectively in order to make accurate assessments and improvements.