Family systems theory rests on three assumptions: the input/output configuration of systems, the concepts of wholeness and subsystems, and the role of boundaries in defining systems. Systems theory focuses on "what happens to the input as it is processed by the system on its way to becoming an output. In addition, it focuses on understanding that the family is a whole. Simply understanding the child with a disability does not mean that you will understand the family, yet understanding the family is necessary for understanding the child and what matters in their life. The last assumption in family system theory is that boundaries are existent between family members and subsystems, and that boundaries are a result of the interaction of family members with each other and from the interaction of the family unit with outside influences.