Fear has promoted knowledge of men more than love has, for fear wants to divine who the other is, what he can do, what he wants: to deceive oneself in this would be disadvantageous and dangerous. On the other hand, love contains a secret impulse to see as much beauty as possible in the other or to elevate him as high as possible: to deceive oneself here would be a joy and an advantage – and so one does so.

– Nietzsche
I thought of that while reading this from Ed Yong:
Whether it’s a drug-addled actor or an almost-toppled dictator, some people seem to have an endless capacity for rationalising what they did, no matter how questionable. We might imagine that these people really know that they’re deceiving themselves, and that their words are mere bravado. But Zoe Chance from Harvard Business School thinks otherwise.
Using experiments where people could cheat on a test, Chance has found that cheaters not only deceive themselves, but are largely oblivious to their own lies. Their ruse is so potent that they’ll continue to overestimate their abilities in the future, even if they suffer for it. Cheaters continue to prosper in their own heads, even if they fail in reality.
She showed that even though people know that they occasionally behave dishonestly, they don’t know that they can convincingly lie to themselves to gloss over these misdeeds. Their scam is so convincing that they don’t know that they’re doing it. As she writes, “Our findings show that people not only fail to judge themselves harshly for unethical behaviour, but can even use the positive results of such behaviour to see themselves as better than ever.”
I like to think of myself as a mostly honest person, to the extent that I would often rather face unpleasant situations than weave a tangled web of deceit to avoid them. But that’s just it; it has just as much to do with the fact that I really prefer my life to be as straightforward and uncomplicated as possible as it does any noble idealism. If I didn’t feel overwhelmed and scattered by having too much to focus on, perhaps I’d get a kick out of lying just to amuse myself with my own cleverness. Of course I’ve lied my ass off in various circumstances, and will probably do so again. But it just so happens that I find it too taxing to have to keep various falsehoods straight in my own head, so I generally prefer to just be up front and deal with whatever results.
In the same way, then, the most efficient and effective liars will be the ones who can mostly convince themselves of their story, enough to not get tripped up by a nervous conscience.
As biological beings who mainly need to feast and fuck (and possibly fight) above all else, it really doesn’t matter if we know ourselves. Plenty of unreflective people do just fine in life when it comes to food and sex and driving off enemies. In fact, you could argue that the examined life, while a goal I personally endorse, can be an onerous burden to impose on oneself for what can often appear to be a negligible payoff. What really matters with regards to advantageousness is how others perceive us, how well we can manipulate them to get what we want and need from them. And sometimes, it might be much more to our advantage to be misleading here, especially if we’re so smooth about it we don’t even consciously notice it anymore.