Orem's Self-Care Deficit Nursing Theory has three related theories: self-care, self-care deficit, and nursing systems. The self-care theory focuses on an individual's ability to care for themselves, while the self-care deficit theory examines when people require nursing assistance. The nursing systems theory describes the relationships needed to provide nursing care. Orem identified universal, developmental, and health deviation self-care requisites and defined a self-care deficit as the inability to meet one's therapeutic self-care demand.