It is theorized that every individual's self-concept - his or her personal understanding of his/her identity - starts with and grows from his/her relationships with other people in his/her life and surroundings.
Children learn to define themselves as having specific kinds of relationships and interactions with parent(s), grandparent(s), and extended family members. A child's birth order within a nuclear family unit influences the way in which the child relates to siblings and to the rest of the world.
Growing from these foundational relationships, individuals expand their circle of relationships to include more people in other kinds of activities which reinforce or alter understandings of roles that any given person comfortably assumes or avoids while in contact with others. The individual's identity is reaffirmed or modified, accepted or challenged as a result of the relationships encountered and continued.