The way to have these conversations is to try to keep them as narrow as possible. You're not trying to explain your worldview, you're just trying to take the other person one step forward in inferential distance. There should be one point that you're trying to make that you want the other person to take away from the conversation, and you should try to make that point as clearly and simply as possible, in a way that will be understandable to the other person. Maybe you can give them a glimpse that there's more to your thinking than just this one point, but only if it doesn't distract from that point.

Bob doesn't do this. He feels that he needs to explain the nature of evidence, he uses an example which is controversial to Rian (and thus is a distraction from the point that Bob is trying to establish with the example), and he responds to every issue that Rian brings up instead of trying to bring the conversation back to the original point. Bob's problem is not that he has particularly unusual or crazy beliefs, it's that he has various views that are different from Rian's and he lets the conversation bounce from one to another without ever sticking with one point of disagreement long enough to get a clear explanation of his views across.