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It's interesting because it takes the big-picture view: rather than focusing on the struggles of an individual person, it notes that we all have some like hardships, and among all those times we can be no more significant than the next person. That can be a difficult view to take on, and a very tough one to express in writing.
Alright, I looked up the definitions to 'Sonder' and 'Onism' to make sure I'd gotten them right. I think something it would do you good to try is experimenting along the lines of having the recognition, that our experiences are not only our own and often no more special than those of the next, that doesn't necessarily have to be a depressing revelation. In fact, it could be comforting to someone who has always seen themselves as the odd one out.
This is a fascinating poem, but slightly more cynical than it needs to be. Maybe trying to write out a more peaceable side to this same epiphany would make a good piece as well.