Steven C. Hayes is a prominent American clinical psychologist and researcher known for his foundational work in behavioral science and psychotherapy with a focus on human language, cognition, and alleviating suffering. He developed Relational Frame Theory (RFT), which explains human higher cognition, and originated Acceptance and Commitment Therapy (ACT), an evidence-based psychotherapy. We explore why our evolution as social primates has left us with a mind that we can’t forget. Dr. Hayes explains how to transition from a life of emotional struggle to one of true psychological flexibility. We also explore the relationship of pursuing happiness and how this may ultimately lead to the opposite, the differences between being in pain and suffering, the concept of experiential avoidance, the concept of cognitive attachment, the evolutionary development of language and human cognition, and the science of developing psychological flexibility.