All of reality cannot be proven although our senses tell us to. This is not a means to disprove reality, but it is relevant. No matter what you experience whether it be insanity, hallucination, what is considered 'reality', and what could 'experience' in a universe with properties differing from this one, it still means that your existence is existent, because you are there. I've never really thought of this before, but actually quote finally makes sense to me, "I think therefore I am".
Your actions in the medium known as reality and their consequences are as of yet consistent, not changing. Achieving any goal requires tools in reality to be used, and reality is, at least this one, is consistent, therefore reusable and learn-able.
What I define as opinion is what one judges to be emotionally or achievement-relatedly satisfying. An opinion is when one has a judgement for an object, abstract or physical, to be correct or useful, without much scientific, as in testing for repeatability, accuracy.
Often emotion can interfere with behavior, even that of behavior that the individual deems correct. This can push an individual to a rash conclusion that the negative emotion associated with the object or idea is deemed false or unworthy.