User blog comment:BF10/There can only be.../@comment-17897872-20140725184302

I am assuming that one door lies and the other tells the truth, I would ask it, "If I would ask the other door which one leads to Reality, what would it say?"

The Reality Door knows that Dreamworld will lie and say that the Dreamworld door is the Reality entrance, so the Reality Door would point at the wrong one. The Dreamworld Door knows that Reality will know that Reality would choose its own door because it always tells the truth. Then it would change its answer to Dreamworld. So both people would point to the wrong door.