"I can give you over forty thousand reasons why I know that sun isn't real. I know it because the emitter's Rayleigh effect is disproportionate to it's suggested size. I know because it's stellar cycle is more symmetrical than that of an actual star. But for all that, I'll never know if it looks real... if it feels real... before this is all over, promise me you'll find out which one of us is the machine." - Cortana
Truly the best thing about H4, something the first trilogy only subtly brushed upon, was the character/relationship driven story between Cortana and John.