Reality is that which, when you stop believing in it, doesn't go away.
~ Philip K. Dick
What I find fascinating in that famous quotation of Dick is that the basic idea is that reality is not something that manifests itself clearly, it's something that doesn't want to go away.
What's the meaning of this? The meaning is that we have a map, a mental map of reality in our head.
And sometimes we superimpose the map that we have in our head, the image of reality that we have in our head, that can be wrong sometimes.
We superimpose it on reality so sometimes we don't really access reality directly. We have our desires, fears, expectations, paranoias, whatever, that act like a sort of filter between [actual] reality -- creating a sort of virtual reality.
That happens for everybody. Well, in a media-saturated society like ours, this is even stronger. We know a match not because we have been there and seen that, we know a lot because we have seen it on TV, on the Internet on some website, or read it in the Wikipedia, and, well, when things do not fit our mental map, mental image, maybe we have touched reality.
That's, I think, what an interpretation can be of that famous statement by Dick.
See also: Rossi, U. (2011). The twisted worlds of Philip K. Dick: A reading of twenty ontologically uncertain novels. Jefferson, N.C: McFarland. http://www.worldcat.org/oclc/692291452