I suspect that on some level, people with some epistemically wrong beliefs actually know that they are wrong. They can talk all day about how the world will end on December 2012, but they don't sell their houses and enjoy the money while they can.

See belief as cheering:

As she recited her tale of the primordial cow, with that same strange flaunting pride, she wasn't even trying to be persuasive—wasn't even trying to convince us that she took her own religion seriously. [...] It finally occurred to me that this woman wasn't trying to convince us or even convince herself. Her recitation of the creation story wasn't about the creation of the world at all. Rather, by launching into a five-minute diatribe about the primordial cow, she was cheering for paganism, like holding up a banner at a football game.

The folks who talked about the world ending in December 2012 weren't really predicting something, in the way they would say "I believe that loose tire is going to fall off that truck" or "I expect if you make a habit of eating raw cookie dough with eggs in it, you'll get salmonellosis." They were expressing affiliation with other people who talk about the world ending in December 2012. They were putting up a banner that says "Hooray for cultural appropriation!" or some such.