Joe Shmoe's determination that "What is Pluto" is a credible source is based on the fact that the source is an article from a reputable website. The website is credible because it is backed by a reputable organization, such as the National Science Foundation. The article is also credible because it is written by an expert in the field of astronomy.
One of the first aspects of an epic poem one examines to learn about the society the poem derives from is the characterization of the hero: specifically, what makes the hero a hero.
