Loneliness is an oppressive state. You know because you’ve been there, just like everybody else. We usually think of loneliness as meaning a lack of human connection but in an existential sense it runs much deeper than that and is a fundamental part of modern human existence. Existential loneliness arises from not having a clear role carved out for you, from not being able to rely on your instinctual apparatus or any other structure to tell you what you’re supposed to do and when you’re supposed to do it.
We tend to look at freedom through rose colored glasses and so we miss the reality that with increasing personal freedom comes increasing personal responsibility to make your own choices, and with this increasing personal responsibility comes increasing loneliness because you truly are alone in the choices you make.
Most organisms act off of their instincts, making them a part of and inseparable from nature, a state where existential loneliness is impossible. Only if you can see yourself as a separate entity can you experience loneliness. The more freedom you have to direct the course of your life the more will this feeling of being separate gnaw away at you. Here we see the appeal of all caste systems. If your role is clearly defined for you and you are completely sure of your place within a society then you feel like you are a part not apart.
The tradeoff of being an intelligent organism aware of itself as a separate entity, capable of making its own choices and directing its own development, is loneliness. You might be able to deal with your loneliness better by deciding this tradeoff is worth it. You get to experience the world like no other type of organism on the planet does or ever has, you get to decide who you are, and this unique relationship to existence means feeling lonely sometimes.