“Above all, don’t lie to yourself.”
Self-deception is presented as especially damaging because it corrupts the person’s ability to recognize truth both inwardly and around them.
Source details
The Brothers Karamazov, Book II, Chapter 4, “A Lady of Little Faith,” Constance Garnett translation, verified against Project Gutenberg #28054 and Wikisource. Father Zossima tells the visitor, “Above all, don’t lie to yourself,” and develops the warning into an argument about self-deception, respect and love; this is fictional character counsel inside the novel.