What about the lies you tell yourself? Aren't you also aware of these? After all, you know when you've had "one too many" of something that's bad for you. It's not pleasant to admit it, but the truth is definitely "out there" (or, in this case, "in here"). An act of self-deception may seem pretty harmless, all things considered, especially when compared to lying to others. But why bother? There's nothing really in it for you other than maybe feeling better in the moment.
A maths lecturer, convinced his wife is cheating, will not check the CCTV footage that might confirm his fears but instead keeps a private tally of the number of pubic hairs she sheds in her underwear. One hair is OK, acceptable, more is evidence that she has been having it off, he says, unaware that he uses these delusions of her infidelity to protect himself from the dangers of intimacy.