If you're at all familiar with Freudian psychology then you'll be akin to the ideas of the id, ego, and superego. Imagine Cortana is the Chief's superego, the dialog that works between the id and the ego. As Cortana deteriorates and goes rampant, the Chief's consciousness, his ego, will be directly exposed to his id, or our instincts that don't care about reality or the needs of others, only its own satisfaction.
Maybe he's not the "strong, silent type." Maybe he's the type that's biting his tongue from telling his superiors to fuck off because he never asked for this.
Holy shit. This explains so much. Seriously. And it actually ties into Halo:CE for me.
There was a part in Halo where after you land in the escape pod, you are supposed to protect these marines at a fort or whatever it is. As I approached, Private Bisenti greeted me: "Thank God you're here, Master Chief... I thought we were in real trouble."
That's when I stuck him with a sticky grenade.
What I did then was go up to every marine and either shoot them, melee them in the back, or whatever it took.
Afterwards, Cortana says something that I found chilling: "We couldn't save them..."
I thought this was Cortana trying to get our story straight for when we had to report to our superiors. But no, it was something far deeper than that. She was trying to smooth things over between my id and ego. It wasn't something to tell everyone else about why they all died. It was something for the Chief to believe.
Didn't I kill all those people? No.
We couldn't save them. She puts "we" in there because, I believe now, she needed to take some of the blame from John in order to keep things working. And also because in that moment, she failed in her role of keeping John's true hatred of humanity at bay.