From the Brothers Karamazov by Fyodor Dostoyevsky

"Above all, don't lie to yourself. The man who lies to himself and listens to his own lie comes to a point that he cannot distinquissh the truth within him, or around him, and so loses all respect for himself and for others. And having no respect he ceases to love, and in order to occupy and distract himself without love he gives way to passions and coarse pleasures, and sinks to bestiality in his vices, all from continual lying to other men and to himself."