How could Sarutobi Itachi have known that, to defend against Genjutsu attacks, Uchiha Brahman had laid down a layer of chakra barrier within his mind?
Ninjutsu: Mind Defense Technique.
With the existence of this Ninjutsu, no matter what kind of Genjutsu it was, it would be useless to him—unless someone could drain his chakra all at once to make him unable to maintain this Ninjutsu. But possessing that kind of ability meant having the power to instantly kill Uchiha Brahman in a flash.
Chapter 76