His mother and Mister Hooper, with their blindness and insensitivity, do not see what is going on between the two boys.

blindness 是名词，由形容词 blind（盲的、看不见的）加上名词后缀 -ness 构成，表示"失明"或"视而不见"的状态。在这里比喻性地表示"故意忽视或不愿看清事实"的意思。