While a child's birth is joyously anticipated, their parents' initial reaction is stress. This, even with a child who is generally considered easy to parent since this pain is both universal and unavoidable.
Beginning at birth, a newborn makes unceasing demands of their parents to become a more effective caretaker. Demands that are critical since a child is dependent on their parents for survival. But the adult mind is conservative and resists the rapid personality change that is needed. This clashing of demands and wills creates parental stress but, slowly, a melding of the needs of both.
An added stress is that a newborn is inserted into an ongoing (family) social system that has developed over time, and must now transform itself to incorporate this unselected newcomer.