Christians (I don't know other books well enough) have said it very well themselves: "Faith is the substance of things hoped for, the evidence of things not seen" Romans something or other - pretty much sums up the problem.
My daughter never really got a good look at a crucifix until she was 3; we were walking by a church and she stopped to look at the one they had displayed out front and said "ewwww!" I asked "what, honey?" she said with revulsion "I don't like that scarecrow!" that's what we call it now: The Scarecrow.
She didn't realize at the time it was any relation to the xtian cross, which we refer to as "their death rune".