As strong as our need for food, shelter and water, connection is something we are wired to want and need. It's an energy exchange; with elements of being seen and heard, and feeling part of a shared human experience. So, it's entirely understandable that we avoid being alone, because of the fear of loneliness accompanying that experience with no mutual exclusivity.
It's like a big, scary monster waiting for us in the dark ready to tackle us the moment we shut ourselves out from the rest of the world. But, like a lot of our emotional thoughts, that story isn't entirely true.