So far as I can tell, there is at least one fact that nearly all believing Christians miss--a very simple fact. That fact is every reading of the Bible is an interpretation.
Whether we're looking at hyper-liberal Anglicanism, evangelical Protestantism, mega-fundamentalist literalism, Christian-Left Catholicism, C.S. Lewis's creedal "mere" Christianity, or anything between or beyond, every one of them requires a reading of the Bible that is an interpretation of the Bible.
When I say "almost all" and "nearly all believing" Christians miss this fact, what I am saying is that to take one's own take on Christianity, however nebulous or strict, as being the truth, one has to miss the fact that it is based upon an interpretation of the Bible. Indeed, that intrepretation of the Bible defines what passes as being "true Christianity" and it is the role of faith to glaze over that fact.
This, then, brings us to the central question posed of all religious believers--a question that they cannot answer: How do you know your interpretation is correct? And it generalizes: How do you know any interpretation is correct?
Every believer in every faith tradition, here focusing on Christianity, has a cherished reading of their scriptural texts, and every believer in every faith tradition has rivals that say that they are wrong. How can these debates and accusations of heresy be settled?
Note that science, depending upon evidence and perhaps a smattering of the philosophy of science, effectively settles interpretive debates eventually. The reason is that they rely upon evidence that becomes less and less subject to varied interpretation the closer one looks.
Now, I've argued before that we cannot know for certain (see Dot, Dot, Dot) that scientific models are "true" descriptions of reality. I'd say all that we can conclude is that they possess sufficient explanatory salience and predictive power to be comfortable calling them "descriptions of reality," carrying the ever-present qualifier of "provisional," where the provisions can be laid out by the philosophy of science and reinforced to some degree by statistical confidence in the predictive power presented.
What matters with regard to these interpretations is that we have a way to claim that we're justified in calling them knowledge. We try to break them on the rock of evidence. To paraphrase the great Richard Feynman, it doesn't matter how beautiful or cherished a hypothesis is or how great the scientist championing it; if it disagrees with evidence, then it is wrong.
Evidence the the final arbiter in science, no matter what. If an idea disagrees with experiment, it is wrong. This is a reality check, and it works wonderfully.
Faith lacks this reality check while pretending it has it, and this is the one fact that almost all Christians miss.
Edit (3 June 2014): William Lane Craig responded to this blog post. Read his response here.
I've written a few thoughts about Craig's response that can be read here.