Statesboro, GA, USA
I think it's more like, "Who defines reality?"
And our definition is challenged, if not daily, then regularly. A run of the gauntlet regarding adaptability, if you will. Since everything is in constant flux proper adjustments must be made.
I think a better term would be "interpret" rather than "define". Reality is not dependent upon our interpretations, but the other way around. That's where adaptability comes in, when we face reality on its own terms.
your opinion on me belongs to my reality. my own opinion is not my reality.
Actually your opinion IS also your reality, unless you deem yourself unreal.
I think what you may be trying to say is that the interpretive content of opinions cannot correspond to reality, hence someone else's opinion becomes reality only by "being" rather than interpreting. But I don't see why one's own opinion would not also be a part of reality. Nor do I see why the interpretive aspect of someone's opinion may either correspond or fail to correspond to reality. That's why we have words like "lie" and "truth", and "right" and "wrong", and "correct", and "incorrect".
It's a necessary way of looking at things unless you want to take the way Nietzsche did, and call all reason and interpretation false, and only pure sensory perception "real". But the moment he did, he lost the right to talk, apart from adding to the noise.