Perhaps it's all in our heads. The opening cinematic is of three astronauts approaching the Traveller. A pilot, a scientist, and a soldier. They stand armed before this amazing entity, and it decides to test them. Since the Traveller is a phenomenally powerful thing, there's no reason to believe that it hasn't psychically invaded the minds of the astronauts to test their worthiness to access its power. The Pilot becomes the archetypical explorer, the hunter. His duty is to confront the worst part of his psyche, the homeless, heartless scavenger, the Fallen. The Soldier is the noble Titan, and his antithesis is the Cabal. Like the Titans, they are soldiers, but unlike the Titans, they fight without a true cause, and follow orders from a source they neither know nor truly question. The Scientist is the Warlock and they must face the Vex. Warlocks seek knowledge to exploit it for the betterment of all. The Vex exist purely to obtain, catalogue, and ultimately lock away knowledge for their own use. Each of these is the opposite face of the coin. The contrasting paradigms. And by confronting themselves in endless mental simulations, the Traveller can judge humanity's worthiness. This can be used to explain the grind of doing missions multiple times. Slight variations in mission parameters can be used in analysis. What happens to the Golden Age? The Collapse? These are mental constructs of our own making so that the true nature of the testing doesn't drive us insane. The mind deceives itself to ensure that it doesn't break. The traveller knows this and projects ghosts into each simulation to provide the mind an escape route from things it knows should kill us, and to monitor us more closely. Races? I have races covered too. Exos are spiritualists, linked to the psychological belief that we were created, and that can't function without that belief. The Awoken represent the atheistic, self made parts of the psyche. They represent those who believe more strongly in free will. Humans are everyone stuck in the middle. Those who are neither constrained by creation, nor bound to a belief in their own superiority. The tower: The tower is a "safe zone" a place where the Traveller can gather our collective experience and results. Compare the cumulative effects of millions of tiny variations in test data. As for The Hive and the Darkness, they are the darkness of the human soul. All of our irrational hatred, our malevolence, our trollish tendencies are represented by the physical Hive and the nebulous Darkness. The Traveller seeks to draw this out of us, force us to confront it, and if we succeed, the golden age it tells us we can remember will be ours. Tl:dr go read something else.