The Allegory of the Cave is an interesting read.
Do things cease to exist just because you don't recognize them?
I know that wasn't the intention, but I think the allegory captured this philosophical question pretty well.
If all you can see are the shadows, and another see the entirety of reality. When you say there are nothing but shadows, you are logically coherent. When the other says the shadows are evidence of another reality, he is logically coherent.
I find this to be the case in most debates on Spiritualism. People who have validly interacted with the realm beyond the physical can't argue with those who haven't... And both are validly convinced of their deductive stations