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, which Itachi encourages whenever they meet. At the same time however, he became determined to do so through his own means, including rejecting Itachi's instructions of obtaining the Mangekyō Sharingan for power, simply to not give Itachi satisfaction.