Egocentrism in theory of cognition is the (axiomatic) assumption that only the cognising subject themselves (i.e. the "ego") exists objectively.
Egocentrism is generally not regarded as a suitable basis for cognition. Anthropocentrism is perhaps the most commonly assumed basis, with pathocentrism, biocentrism and holism being possible alternatives.
Egocentrism and Power
Obtaining power over others, and thus instrumentalising others, may be interpreted as an attempt to make the real world, in which multiple autonomous human subjects live, conform to the egocentric model of the person who seeks power.