Just as a satisfaction of instinct spells happiness for us, so severe suffering is caused us if the external world lets us starve, if it refuses to sate our needs. One may therefore hope to be freed from a part of one's sufferings by influencing the instinctual impulses.
Sigmund FreudThe functional importance of the ego is manifested in the fact that normally control over the approaches to motility devolves upon it. Thus in its relation to the id it is like a man on horse back, 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.
Sigmund Freud