Itachi offered water to an ailing Iwagakure shinobi(Earth), after drinking the water, he noticed that itachi had weapons, hence tried to kill him.
But, luckily his father Fugaku Uchiha arrives in time and saves him by killing the Iwagakure shinobi.
This incident had a huge impact on Itachi. He was traumatized and hated war. Furthermore, he met Orochimaru after the war was concluded who told him that Life without eternity is meaningless.
Itachi and Shisui – The Eternal Friendship
At the age of 5, he became friends with Shisui Uchiha who was another genius in Konoha. Shisui taught Itachi a great deal about life and how a shinobi should live his life.
As Itachi was able to use both the Kage-bunshin jutsu and the fireball jutsu, he graduated the academy at the tender age of 7!
Yes, he became a genin at the age of 7 ( Naruto was 13 when he became genin).
He activated his Sharingan at the age of 8 after he witnessed the killing of his teammate Tenma Izumo by a Masked man. He became a chunin by the age of 10, then went on to be an ANBU captain at the age of 13. That’s Itachi Uchiha for you!