I've heard it said that "you are the universe experiencing itself." It was always an interesting thing to hear, but it took quite a while before it finally sank in. When I finally 'got it', it was an amazing realization.
As an individual, we are intimately familiar with ourselves. We hear all of our thoughts and know all of our secrets. But more importantly, we cannot hear anybody else. We are deaf to the rest of humanity, which makes us feel separate and isolated from the universe.
The universe, though, is quite literally everything. Every atom is part of the universe, as are all the things that make up atoms, and all the things that atoms make up. I am as much a part of the universe as a squirrel or a flower or a comet (and so are you). In this context, we are quite literally the universe experiencing itself.
Even in a more simplistic sense, people have a habit of considering themselves separate from the world around them. They work for a company, but they are not part of the dynamic system that is the company. They live in a city, but the city exists whether or not they live there.
Oddly enough, despite how hardwired people are to create communities, humans seem to struggle to see themselves as a crucial component to the make-up of the communities they live in.