Humans suffer the most because we are aware of our own suffering. I would contend that a cow, in captivity, would not think to itself, “These living conditions are inhumane and terrible and I have been robbed of my own individuality and freedom.” No, the cow thinks, “Look, there is food.”
This is the difference between the human and the animal, the fact of the matter is that the human is aware of its own existence, and thereby the existence of its own suffering, and of suffering because of the awareness of its suffering. By contrast, the animal has no thoughts of itself, it only thinks in terms of what is in front of it and what causes it pain.
Humanity being aware of themselves on the individual level has also led to a lot of problems, as sometimes, especially in the modern age, to fully express oneself as an individual in the sea of 8 billion plus people due to this awareness, is an impossible task. Because humanity is aware of itself individually, it also comes a need to express that individuality, becoming what we would call hobbies, but hobbies are not just things that people do to pass the time, they are an expression and expansion of oneself.
But as with all things, there is an opposite, and the opposite to the expression of this individuality is the comforting hand of conforming. This hand leads most people in their lives, as most everybody likes to feel like they belong.
Along with this however, is the feeling of homogeneousness that comes with the pleasures of conformity, a feeling that is foreign to me, not to say that I have not felt it, but when I do, I instantly turn away, as I feel my individuality start to slip away. It makes me feel as though I am no longer Johnathan Schmidt, the man, but Johnathan Schmidt, the person who is part of a larger puzzle, and it is unsettling. This is not to say that being an active member within a community is bad, I am only talking about when a person is defined by the organization they are a part of is when they are stripped of their individuality.
All of this melancholic rambling about loneliness and homogeneousness is but one part of this awareness of existential suffering. There is good reason as to why dozens, if not hundreds of books have been dedicated to the attempted explanation of existential suffering. Most of them only try to sum up one aspect of it. If someone were able to fully explain and give each concept the time that they deserve, the person who did that would have to live to extraordinarily old age just to write it at a level that is acceptable for most academic communities.
Consider this piece a rambling about existential human suffering and how we are the worst-off species on the planet due to our awareness of the suffering and the need to express our individuality because of it.