We are social creatures and every human group (family, tribe, clan, class, country, nation, state) we belong to has a story about itself and about the people and places beyond its boundaries and borders. Arjun Appadurai put it quite well when he pointed out that "No modern nation, however benign its political system and however eloquent its public voices may be about the virtues of tolerance, multiculturalism, and inclusion, is free of the idea that its national sovereignty is built on some sort of ethnic genius."
These stories contain facts mixed with myths to form powerful narratives and we cannot help but evaluate the input we get from the world against the storyline of whatever group we identify with. Even the most indepdendent of thinkers can find himself struggling mightily to incorporate information that challenges what he thinks he already knows about the world. Those who are quick to recognize this about religion or nationalism should acknowledge that there are quasi-religious narratives lurking under the surface of their "rationality". As Mircea Eliade said:
"Mythical behaviour can be recognized in the obsession with 'success' that is so characteristic of modern society and that expresses an obscure wish to transcend the limits of the human condition; in the exodus to Suburbia, in which we can detect the nostalgia for 'primordial perfection'; in the paraphenalia and emotional intensity that characterize what has been called 'the cult of the sacred automobile.'"These stories are another impediment to seeing the world clearly because challenging them (and finding them wanting) gets us kicked out of a club we desperately wish to belong to. Most groups (even ones comprised of "free thinkers") do not tolerate even small deviations from the common story. Is it not true that perceived apostates are treated even more harshly then those who are clearly in the camp of the enemy? Every group has its own Inquisition, ready to ferret out those who "belong without believing."
So I would add this heuristic to the list - one that was beautifully expressed by the late Christopher Hitchens - "How do I know that I know this, except that I've always been taught this and never heard anything else? How sure am I of my own views? Don't take refuge in the false security of consensus, and the feeling that whatever you think you're bound to be OK, because you're in the safely moral majority."