I think by cornerstone, they are referencing that beliefs are assumptions that form one’s model of the world.

You think by logically building on assumptions. “I remember putting leftovers in the fridge last night, so I don’t need to make dinner tonight” You assume your memories are accurate (or accurate enough) and then build on other things you “know” to construct every thought.

Sights, sounds, and vibes are a different story. They are called qualia and the raw experience of them cannot be described.

Think of qualia like the raw data you collect from an experiment. Your worldview is the scientific model you’ve built to describe this data and it rests on both fundamental logic and the beliefs/theories you currently believe in.

Unfortunately people don’t like having to change their worldview. And when you’ve held a belief for long enough, it becomes foundational to many of your other assumptions. Some people would rather say reality is wrong than change their beliefs.

The word for a belief that cannot be changed via evidence is called a “delusion” in case you ever want to piss off a religious person who says “nothing can shake my faith” like it’s a good thing.

Sounds like the idea of "belief" is just being accepted as a religious or spiritual idea. Beliefs are the cornerstone because it's a tool we use every single day.

At the center of how we think is the fundamental idea of The Way Things Work and that comes down to how we believe the physical things around us will act and react. Just about everyone will start making a choice by comparing what we know to be real or true for ourselves and the things around us.

That cornerstone of belief is what we use to define "real and true". Ghosts or spirits are absolutely real and true for some people while others don't see the same evidence.

Beliefs get the special treatment because we are a collection of our experiences and each one of us has a different way of understanding how things work.