Everything about individual life forms surviving on Earth boils down to one imperative: each living cell is trying to keep other cells out (unless it's also part of the same being, and then as I understand it very rarely). Life builds walls around tiny amounts of water, cell by cell, then does its best to hang onto itself while other living things try to sneak inside and either pillage for fuel and water or take over the joint for its own purposes, like a virus does. It's not all cutthroat: symbiosis is everywhere*. But cells strive to keep their borders up, even if they're cuddled up really close, like the two species that make up a lichen. Even if they absolutely need each other to survive, there are either mechanisms that let a cell identify another cell as a part of the larger being, or the cell rejects all other cells outright. Beings like us even have hoards of cells that prowl around for cells that aren't ours and kill them.
Most of this is 'no duh'. I know. It's just a trippy realization: the whole reason you are alive right now is that all of your cells are constantly saying "No!" to all other cells. "No you may not have this water." Or, "This is my molecule of iron. There are many like it, but this one is mine."
It's fun (though far-fetched) to think about how that might affect us psychologically, or if you're into that, spiritually. We spend a lot of our lives trying to reach out to others. To make a connection, and to affect or be affected. Often, it feels as good to have our brains polluted with new concepts as it does to pollute others'. But rule number 1 is always to keep everyone else out. That's an awesome dichotomy of life.
*Did you know that the number of harmless/helpful bacteria living in your gut is almost as large as the number of human cells that constitute you? You're almost outnumbered, even now. :3