When Itachi murdered the rest of the Uchiha clan, Sasuke was crushed not only by the loss of his family but also by what Itachi told him: that he had never loved Sasuke. Sasuke devotes years of his life to avenging their family by killing Itachi. With his new outlook, he became cold toward others, unmoved by and uninterested in what they do or think of him, choosing instead to keep to himself. He stopped using honourifics. His only goal in life became to take revenge for his clan's deaths.