The ego or egocentrism is the inability to differentiate between the self and the other. More specifically, it is the inability to disentangle subjective patterns from objective reality. An inability to understand or assume any other perspective than their own.

Jean Piaget argued that young children are self-centered. This in no way means that they are selfish, but they still do not have enough mental ability to understand other people who may have different opinions and beliefs regarding their own. Piaget did a test to investigate egocentrism called the study of mountains. He put the children in front of a simple plaster saw and asked them to choose, from four portraits, the vision that he, Piaget, would see. The younger children chose the portrait of themselves that they were looking at. However, this study has been criticized, justifying that it is simply the knowledge of the children’s spatial vision and not of egocentrism. A subsequent study involving police puppets showed that young children were able to correctly say what the interviewer was looking at. Presumably Piaget overestimated the levels of egocentrism in children.

Although egocentrism and narcissism seem similar, they are not the same. A person who is self-centered believes that they are the center of attention, like a narcissist, but receives no gratification from their own admiration. Both egoists and narcissists are people whose egos are greatly influenced by the approval of others, while for egocentrists this may or may not be true.

Although self-centered behaviors are less prominent in adulthood, the existence of some forms of self-centeredness in adulthood indicates that overcoming self-centeredness may be a lifelong development that never reaches completion. Adults appear to be less egocentric than children because they are quicker to correct from an initially egocentric perspective than children, not because they are less likely to initially adopt an egocentric perspective.

Therefore, self-centeredness is found throughout life: in early childhood, adolescence, and adulthood. It contributes to human cognitive development by helping children develop theory of mind and self-identity formation.