The assumptions that humans are intelligent and self-aware, and can understand each other are often left unspoken because actually pretty hard to support with anything but the subjective experience of "Well, I certainly am self-aware, and possess of intellect, and can understand and be understood by other people who obviously are also self-aware, intelligent, and can understand me and can be understood by me". Ha, "people understand each other", what a joyous fiction! Any one who ever attended any meeting with customers or high officials, or parents of your S.O. can attest to the opposite.