The fear of the unknown is universal. Without being able to identify something, you cannot classify it as either safe of dangerous. To defend against this, you must learn. But in Yharnam, to learn is to ensure madness.
The city is beset by a beast plague. Men and women lose their minds, grow hairy and violent, and then try to kill their neighbors.
The only ones who stand a chance against the beasts are the hunters, specialists trained to hunt beasts. Supposedly, these hunters can end up coated in beast blood, but never succumb to the plague. Yet, throughout the game, more than a dozen hunters are encountered, and very few of them are still sane.
Why? What causes citizens to become beasts? Why do those sworn to protect to turn on each other?
The answer is truth.
The longer a hunter goes, the more they truly “see” the world. That which was unknown becomes known. In Yharnam, that is a horrifying fate.
As you progress through the game, you earn something called “insight”. This is earned through items called “Madman’s knowledge” and through encountering and defeating bosses. It is thought that to keep yourself from succumbing to the plague, you must have knowledge. You must be able to see the world as it truly is, not just with your eyes, but with your mind. You need eyes, eyes on the inside. As your insight increases, elements of the game change.
The most striking example is an area of the game known as the Cathedral Ward. By this point in the game, the Cathedral Ward is a place of safety, a place to come back and rest after dealing with the world of monsters outside. The incense burning there keeps beasts away. Just outside the cathedral meant to act as a safe haven for citizens not affected by the beast plague, there is a certain spot. With low insight, standing in that spot will cause a blue aura to float down to you and lift up, holding you for a second, damaging your character, and dropping them. But much later in the game, as soon as your insight hits 40, you see what is actually happening.
The blue aura is not just an aura, it is a hand. You are grabbed by a massive eldritch creature known as an Amygdala with a head like a pumice stone and six long, gangling arms. This massive, spidery horror as been looming just over you, watching with its many eyes when you thought you were safe.
This is by no means the only instance of insight changing the game. New enemies can appear, old enemies gain new abilities or do more damage. A certain enemy type can suddenly be heard singing in an off-key tone.
As you progress further through the game, you learn more and more about the nature of the world. You come to entire other plains of existence with twisted geography, stones with viscera inside, and twisted distorted creatures.
The more you learn, the uglier the world becomes. You learn about the beings knowns as “Great Ones”, creatures from other worlds that came and began to affect humanity. The hunters were formed by a union with one of them. The beast curse has some connection to their presence. The world is coming apart simply by humanity’s encounter with them. Not knowing is dangerous, but there are answers not meant to be learned, truths no meant to be known, and when humanity went looking for those answers and truths, they encountered something they were not read for. In Yharnam, there is no peaceful ending. Insanity is, sadly, inevitable.