Generally my sense is that people are not good at measuring their expertise about topics. We infer a lot of data into our world views based on paltry facts and analogy to our own experiences. We think we understand because our minds paper over the lacuna of our knowledge. The more I learn, the more I realize how little I know, and how quick people are to believe that other people's experience is much like their own.

That's why I ask people to cite sources often, or listen to their personal stories, so I can learn more.