As Freud moves outward from his early work on the pleasure principle and the role of the libido in human motivation, he becomes increasingly convinced that the inherent drive of the psyche is that of equilibrium. He explores this first by showing how the pleasure principle and the reality principle strike a balance in the human psyche, leading to the moderation of pleasure and reality. 

The pleasure principle, in which the libido functions, is housed in the id, or the unconscious. Freud’s early works showed how children and adults were driven to seek pleasure and avoid pain. However, pleasure-seeking often stands in contrast with the superego, which adheres to social expectations, norms, and systems of morality. Therefore, the ego must seek balance between the superego and the id by repressing desires and delaying gratification. It is the work of the psyche to maintain this balance:

The facts which have caused us to believe in the dominance of the pleasure principle in mental life also find expression in the hypothesis that the mental apparatus endeavours to keep the quantity of excitation present in it as low as possible or at least to keep it constant.