We can establish an epistemological concept of objective realty that follow the rules of formal logic. It does mean we may always try to improve on this and fill holes. Objective reality or at least an estimate of it can be established , it's important so we don't loose touch with our rationality. In an ontological sense we can only prove our own subjective reality but not others, but that still only leads to agnosticism, it proves the self but doesn't prove that others do not exist , it would be unwise in my opinion to treat others like they do not truly exist or go through life ignoring rational thinking. It often leads to egoism and just loosing grip with compassion for others etc witch isn't productive. There is a youtuber "destiny" with the most bizarre moral system based on that ideology, no matter how constituent it may be it's rejected as absurd by others.
It's a really cool thing to think about tho one of those big questions in philosophy.
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