(This article expands upon my response to a question posed by pjeby here)

I've seen a few back-and-forths lately debating the instrumental use of epistemic irrationality -- to put the matter in very broad strokes, you'll have one commenter claiming that a particular trick for enhancing your effectiveness, your productivity, your attractiveness, demands that you embrace some belief unsupported by the evidence, while another claims that such a compromise is unacceptable, since a true art should use all available true information. As Eliezer put it:

I find it hard to believe that the optimally motivated individual, the strongest entrepreneur a human being can become, is still wrapped up in a blanket of comforting overconfidence. I think they've probably thrown that blanket out the window and organized their mind a little differently. I find it hard to believe that the happiest we can possibly live, even in the realms of human possibility, involves a tiny awareness lurking in the corner of your mind that it's all a lie.

And with this I agree -- the idea that a fully developed rational art of anything would involving pumping yourself with false data seems absurd.

Still, let us say that I am entering a club, in which I would like to pick up an attractive woman. Many people will tell me that I must believe myself to be the most attractive, interesting, desirable man in the room. An outside-view examination of my life thus far, and my success with women in particular, tells me that I most certainly am not. What shall I do?

Well, the question is, why am I being asked to hold these odd beliefs?  Is it because I'm going to be performing conscious calculations of expected utility, and will be more likely to select the optimal actions if I plug incorrect probabilities into the calculation? Well, no, not exactly. More likely, it's because the blind idiot god has already done the calculation for me.

Evolution's goals are not my own, and neither are evolution's utility calculations. Most saliently, other men are no longer allowed to hit me with mastodon bones if I approach women they might have liked to pursue. The trouble is, evolution has already done the calculation, using this now-faulty assumption, with the result that, if I do not see myself as dominant, my motor cortex directs the movement of my body and the inflection of my voice in a way which clearly signals this fact, thus avoiding a conflict. And, of course, any woman I may be pursuing can read this signal just as clearly. I cannot redo this calculation, any more than I can perform a fourier analysis to decide how I should form my vowels. It seems the best I can do is to fight an error with an error, and imagine that I am an attractive, virile, alpha male.

So the question is, is this self-deception? I think it is not.

In high school, I spent four happy years as a novice initiate of the Bardic Conspiracy. And of all the roles I played, my favorite by far was Iago, from Shakespeare's Othello. We were performing at a competition, and as the day went by, I would look at the people I passed, and tell myself that if I wanted, I could control any of them, that I could find the secrets to their minds, and in just a few words, utterly own any one of them. And as I thought this, completely unbidden, my whole body language changed. My gaze became cold and penetrating, my smile grew thin and predatory, the way I held my body was altered in a thousand tiny ways that I would never have known to order consciously.

And, judging by the reactions, both of my (slightly alarmed) classmates, and of the judges, it worked. 

But if a researcher with a clipboard had suddenly shown up and asked my honest opinion of my ability as a manipulator of humans, I would have dropped the act, and given a reasonably well-calibrated, modest answer.

Perhaps we could call this soft self-deception. I didn't so much change my explicit conscious beliefs as... rehearse beliefs I knew to be false, and allow them to seep into my unconscious.

In An Actor Prepares, Bardic Master Stanislavski describes this as the use of if:

Take into consideration also that this inner stimulus was brought about without force, and without deception. I did not tell you that there was a madman behind the door. On the contrary, by using the word if I frankly recognized the fact that I was offering you only a supposition. All I wanted to accomplish was to make you say what you would have done if the supposition about the madman were a real fact, leaving you to feel what anybody in the given circumstances must feel. You in turn did not force yourselves, or make yourselves accept the supposition as reality, but only as a supposition.

Is this dangerous? Is this a short step down the path to the dark side?

If so, there must be a parting of ways between the Cartographers and the Bards, and I know not which way I shall go.