Related to: Will your real preferences please stand up?
Last week I read a book in which two friends - let's call them John and Lisa so I don't spoil the book for anyone who wanders into it - got poisoned. They only had enough antidote for one person and had to decide who lived and who died. John, who was much larger than Lisa, decided to hold Lisa down and force the antidote down her throat. Lisa just smirked; she'd replaced the antidote with a lookalike after slipping the real thing into John's drink earlier in the day.
These are good friends. Not only was each willing to give the antidote to the other, but each realized it would be unfair to make the other live with the crippling guilt of having chosen to survive at the expense of a friend's life, and so decided to force the antidote on the other unwillingly to prevent any guilt over the fateful decision. Whatever you think of the ethics of their decision, you can't help admire the thought processes.
Your brain might be this kind of a friend.
In Trivers' hypothesis of self-deception, one of the most important functions of the conscious mind is effective signaling. Since people have the potential to be excellent lie-detectors, the conscious mind isn't given full access to information so that it can lend the ring of truth to useful falsehoods.
But this doesn't always work. If you're addicted to heroin, at some point you're going to notice. And telling your friends "No, I'm not addicted, it's just a coincidence that I take heroin every day," isn't going to cut it. But there's another way in which the brain can sequester information to promote effective signaling.
Wikipedia defines the term "ego syntonic" as "referring to behaviors, values, feelings that are in harmony with or acceptable to the needs and goals of the ego, or consistent with one's ideal self-image", and "ego dystonic" as the opposite of that. A heroin addict might say "I hate heroin, but somehow I just feel compelled to keep taking it." But an astronaut will say "I love being an astronaut and I worked hard to get into this career."
Both the addict and the astronaut have desires: the addict wants to take heroin, the astronaut wants to fly in space. But the addict's desires manifest as an unpleasant compulsion from outside, and the astronaut's manifest as a genuine and heartfelt love.
Suppose that in the original example, John predicted that Lisa would ask for the antidote, but later feel guilty about it and believe she was a bad person. By presenting the antidote to Lisa in the form of an external compulsion, he allows Lisa to do what she wanted anyway and avoid the associated guilt.
Under Trivers' hypothesis, the compulsion for heroin works the same way. The heroin addict's definitely going to get that heroin, but by presenting the desire in the form of an external compulsion, the unconscious saves the heroin addict from the social stigma of "choosing" heroin. This allows the addict to create a much more sympathetic narrative than the alternative: "I want to support my family and keep clean, but for some reason these compulsions keep attacking me," instead of "Yeah, I like heroin more than I like supporting my family. Deal with it."
EGO SYNTONIA, DYSTONIA, AND WILLPOWER
Willpower cashes out as the action of ego syntonic thoughts and desires against ego dystonic thoughts and desires.
The aforementioned heroin addict may have several reinforcers both promoting and discouraging heroin use. On the plus side, heroin itself is very strongly rewarding. On the minus, it can lead to both predicted and experienced poverty, loss of friendships, loss of health, and death.
Worrying about the latter factors determining heroin use - the factors that make heroin a bad idea - is socially encouraged and good signaling material. A person wanting to put their best face forward should believe themselves to be the sort of person who cares about these things. These desires will be ego syntonic. Wanting to take heroin, on the other hand, is a socially unacceptable desire, so it presents as dystonic.
If the latter syntonic factors win out over the dystonic factors, this feels from the inside like "I exerted willpower and managed to overcome my heroin addiction." If the dystonic factors win out over the syntonic factors, this feels from the inside like "I didn't have enough willpower to overcome my heroin addiction."
DYSTONIC DESIRES IN ABNORMAL PSYCHOLOGY
There is some speculation that the brain has one last trick up its sleeve to deal with desires that are so unpleasant and unacceptable that even manifesting them as external compulsions isn't good enough: it splits them off into weird alternate personalities.
One of the classic stereotypes of the insane is that they hear voices telling them to kill people. During my short time working at a psychiatric hospital, I was surprised by how spot-on this stereotype was: meeting someone who heard voices telling him to kill people was an almost daily occurrence. Other voices would have other messages: maybe that the patient was a horrible person who deserved to die, or that the patient must complete some bizarre ritual or else doom everybody. There were relatively fewer voices saying "Hey, let's go fishing!"
One theory explaining these voices is that they are an extreme reaction to highly ego dystonic thoughts. Some aspect of the patients' mental disease gives them obsessive thoughts about (though rarely a desire for) killing people. Genuinely wanting to kill people would make you a bad person, but even saying "I feel a strong compulsion to kill people" is pretty bad too. The best the brain can do with this desire is pitch it as a completely different person by presenting it as an outside voice speaking to the patient.
Although everything about dissociative identity disorder (aka multiple personality disorder) is controversial including its very existence, perhaps one could sketch a similar theory explaining that condition in the same framework of separating out dystonic thoughts.
A conscious/unconscious divide helps signaling by allowing the conscious mind to hold only socially acceptable beliefs, which it can broadcast without detectable falsehood. Socially acceptable ideas present as the conscious mind's own beliefs and desires; unacceptable ones present as compulsions from afar. The balance of ego syntonic and dystonic desires presents as willpower. In extreme cases, some desires may be so ego dystonic that they present as external voices.