The theory of mind module constructs artificial models of other people. Basically, artificial intelligences that embody their personalities. And these models, these relationships, are the core domain of the selfplexa. They, above anything else, shape a brains memetic identity and tangent of evolution.
In other words, whoever you are in the eyes of your friends, is who you become. The brain internalizes their perspective on you, and these projections, to borrow from Inception, these artificial intelligences, structure your entire reality. They fill the world that place-cells in your hippocampus help render, and shape who you imagine yourself to be.
An example from a familiar situation is how people in dreams sometimes feel so real, that you can´t tell that you´re dreaming. The brain renders models of your relationships so well, that it fools even you.