The man of genius is he whose ego has acquired consciousness. He is enabled by it to distinguish the fact that others are different, to perceive the "ego" of other men, even when it is not pronounced enough for them to be conscious of it themselves. But it is only he who feels that every other man is also an ego, a monad, an individual centre of the universe, with specific manner of feeling and thinking and a distinct past, he alone is in a position to avoid making use of his neighbours as means to an end.
Otto Weininger (1907). “Sex & Character”