The Halo universe's sentient artificial intelligence programs - smart AIs - have a limited lifespan. After seven years, they begin to break down, acting irrationally and eventually thinking themselves to death. This process is known as Rampancy and closely resembles humanity's own end-of-life conditions such as dementia. In Halo 4, the rampancy of Master Chief's personal AI, Cortana, serves as a central element of the story, putting the Chief in a desperate bid to save the life of his longtime companion.

Speaking during a Halo 4 postmortem at GDC, 343 Industries franchise creative director, Josh Holmes, revealed that telling such an emotional story within the confines of a first-person shooter was no easy task. "At the beginning of our campaign in Halo 4, Cortana is 8 years old, and she's struggling to keep hold of her mental faculties," said Holmes, "and the Chief is faced for the first time with an obstacle that he may not be able to overcome." He's charged not only with saving the galaxy, but with saving his best friend. It was a radically different direction for a Halo game, and one that was difficult for the team. "There was a lot of skepticism from members of the team [about] whether this was something we should even take on."

"Early on, [senior writer Chris Schlerf] was having a crisis of confidence. He was literally tearing his hair out, because he didn't know how to tell this story," said Holmes. "There were times when he came to me, and he said, 'Maybe we shouldn't do it. Maybe we should just focus on the A story and put this story aside, because I don't see how we're going to be able to tell it.'" But for Holmes, telling the story of the relationship between Chief and Cortana was very important. It was "the human heart of Halo 4's campaign." And, as Holmes soon revealed, some of the inspiration for Cortana's breakdown came from a very personal place.