If you don’t know, when Itachi was only 13 years old, he was given the task to kill everybody in the entire clan because his father wanted to stage a coup and take over the Leaf Village.
Itachi was 13 years old, he was a child and these grown adults were tasking a child to commit a mass murder against his family, friends, and clan.
Itachi kept this to himself, but if we are looking at things realistically, this entire situation is messed up.
And yes, Itachi was wise well beyond his years, but mentally, there’s no way Itachi was able to kill his entire clan and was able to walk away, going along with his life. He was deeply hurt inside, and I believe one of the biggest mistakes Itachi ever made was not taking Sasuke with him.