answer:Experiences in the formative years define individuals because they most often occur when said individual is still mentally developing and thus make a huge impression. Aside from that, I think you answered your own question with this quote: “Why do you suppose things from the past continue to be the backboard from which we measure the rest of our lives?” Humans love comparison. We like to use established events and feelings as a measuring stick or a comparative for other similar events, feelings, and ideas.