Id, ego, and super-ego
"The ego is that part of the id which has been modified by the direct influence of the external world ... The ego represents what may be called reason and common sense, in contrast to the id, which contains the passions ... in its relation to the id it is like a man on horseback, who has to hold in check the superior strength of the horse; with this difference, that the rider tries to do so with his own strength, while the ego uses borrowed forces".363/4