"It is this fragility that makes deception so very easy up to a point, and so tempting. It never comes into a conflict with reason, because things could indeed have been as the liar maintains they were. Lies are often much more plausible, more appealing to reason, than reality, since the liar has the great advantage of knowing beforehand what the audience wishes or expects to hear. He has prepared his story for public consumption with a careful eye to making it credible, whereas reality has the disconcerting habit of confronting us with the unexpected, for which we were not prepared.
Under normal circumstances, the liar is defeated by reality, for which there is no substitute; no matter how large the tissue of falsehood that an experienced liar has to offer, it will never be large enough, even if he enlists the help of computers, to cover the immensity of factuality. The liar, who may get away with any number of single falsehoods, will find it impossible to get away with lying on principle."
Another point is how the liar may be so drawn into the fabric of his own lies that he is no longer able to perceive reality. He honestly beleives his own fantasyland is true. Then the danger becomes that others will also cling to the lie because they trust the self-deceiving sincerity of the liar more than they trust the evidence on the table before them. The liar's story tells them what they want to hear.
Kerry/Edwards - 2004 - Leaving fantasyland behind