Tying in with the whole truth thing is how do we know what we are experiencing is the truth? In the car business they say there are three sides to a story - the buyer's, the seller's and the truth. This, obviously, is the same in everything. I sat in a meeting today and took notes. What I wrote down was not a transcript, but my interpretation of what was said by the participants. They will have their own interpretations. Unfortunately, this allows people to deny later what they agreed too.
I had a professor in college, a grad student really, who described the simplest philosophical experiment. How do you know that you are not really a brain in a vat being fed sensory data? You don't, because your brain believes it is living in a world that may be false. An extension of this is the "Lathe of Heaven" argument. In this book, whatever the protagonist dreams becomes the world he is living in. How do you know that every day your world is not changing a little and today's reality is not yesterdays?