Honest people are the best liars.
A truism of the human condition. Everyone lies, even if it is unintentional. The true masters of the art are the honest ones; they can remember what they said to one person and make sure they don't contradict themselves when talking to another. Their mind carefully ticks and tocks, mainting a delicate equilibrium of deciet.
Almost all lies are discovered by one person knowing something that clashes with what someone else knows. One of them has been told a lie. An "honest" person carefully articulates his lies, making sure that they all fit together to form one large false mosaic, rather then several false conflicting mosaics that can lead to the discovery of the lie.
Thus, it is important to handle only one lie with any one population at a time if the lies contradict each other, because with each contradicting lie you increase the chance that somebody will unearth your falsities.
The reason this technique is so often succesfull, lies in a bit of egoism. Tell people what they want to hear, and they'll think you're honest. Tell people what they don't want to hear, and you call them to action, doing exactly what you hoped they would.