When a person cannot deceive himself the chances are against his being able to deceive other people.

Mark Twain

It is the nature of ambition to make men liars and cheats, to hide the truth in their breasts, and show, like jugglers, another thing in their mouths, to cut all friendships and enmities to the measure of their own interest, and to make a good countenance without the help of good will.

Sallust

One must not cheat anyone, not even the world of its victory.

Franz Kafka