Why do humans believe things? Why do we venture into thought worlds that can only exist through exerting a high level of belief that can't be substantiated by materialistic, visible processes?
Because we evolved that way.
Part of what makes humans successful is the ability to teach and receive information and ideas without having personally experienced the knowledge firsthand. We learn from each other, not just through observing another person's actions, but through the other person recounting a lesson, or a bit of knowledge, or a new way of doing things.
We store up all this information in our relatively large brains and it gives us an advantage we wouldn't have otherwise. We survive because we are good at information storage, retrieval, and analysis.
A large portion of that information we must accept on faith. There's no way we could personally check every fact or idea for veracity. There must be a level of trust present in our learning; trust from our teachers, from our fellow humans, and in the process of learning itself.
This trust is self-reinforcing. When we receive a new bit of information, or advice about something, and we follow it and it turns out to be true and right, then we have strengthened the level of trust we have for secondhand knowledge.
Multiply this by a million instances and it's easy to see how trust and belief become natural human tendencies. Because we are social animals living in complex social hierarchies, it is a necessity that we trust each other and build upon a base of knowledge that is shared across our social group regardless of our ability to prove that the conglomeration of ideas that guides our lives is true in every detail.
Belief, then, is just a normal outgrowth of our development and survival as a species.
Of course, that's the positive side of belief and trust, but belief and trust can go horribly awry. It's possible to believe things which are false. It's possible to be manipulated and have belief and trust misused and abused by a devious person. It's possible for belief to become our main way of viewing the world to the exclusion of the reality around us.
In turn, it seems to me that belief--the acceptance of ideas that we haven't personally verified--is directly tied to our social groupings and loyalties. And, when our beliefs are challenged, the ramifications are enormous for us because of what it does to our sense of unity and trust in the larger system in which we exist.
Logically, it would seem silly to be so critically affected by an overturned belief. After all, everyday we have to adjust to new circumstances and learn from our failures. If I think the best way to get across town is route A and I've been going that way all my life, and everyone I know swears by that route, I don't get upset or feel ashamed if I learn that route B is actually faster and more convenient. I simply start using route B and wind up happy that I learned something new.
Yet this doesn't happen when we experience it in our religious or personal beliefs. Changing or losing belief in these areas is monumental because of what it says about our trust and attachment to a particular group of people, people we feel close to and love and interact with every day. People who we used to listen to uncritically and trust implicitly.
Because what we have learned in life has always come down to us through our closely knit social groups, there is no way to overturn a deeply held, core idea without it appearing treasonous to the group, without seeming to undermine the authority of the very group which produced us.
more on this later.....