Final answer:
Carl Rogers attributes the development of his theory to the concept of unconditional positive regard, which is foundational to his humanistic psychological theory and client-centered therapy.
Step-by-step explanation:
Carl Rogers gives most of the credit for the development of his theory to the concept of unconditional positive regard, which emphasizes the importance of being accepted and prized to develop a caring attitude towards oneself. This approach is central to his humanistic psychological theory and his client-centered therapy. It is through the process of being given unconditional positive regard that individuals can develop congruence between their ideal self and real self, leading to higher self-worth and a more productive life.