Why Did Itachi Uchiha Die With a Smile in ‘Naruto Shippuden’?

Despite Itachi’s considerable skills, he is quickly approaching his limit by the time he and Sasuke begin their final fight. His mastery over the Mangekyō Sharingan would soon lead Itachi to blindness, and the only way to prevent this was to steal his brother’s eyes.

This places them on even ground as the two of them exchange blows using their respective ninjutsu mastery. Eventually, Itachi gains the upper hand, but only after expending an immense amount of chakra.

Source: https://www.distractify.com/p/why-did-itachi-die-with-a-smile