By your terms, NOTHING is possible unless it is shown.
Well, imagine it from the contrary perspective. How do you propose to tell the difference between the things that are possible but haven't happened yet, and the things that haven't yet happened because they're impossible and will therefore never happen?
You can make reference to a wider body of knowledge, say physics, and conclude that a certain thing is likely not possible because it would mean that all our physics knowledge is wrong. But it's likely that our physics is wrong, at least partially, so what does that prove?
Epistemological modesty means making the minimal, most defensible conclusions.
Epistemological modesty means not concluding any more than what there is evidence for.
I realize you don't understand it. It gets back to your problem with evidence: you don't understand what it means when a proposition is supported by evidence. That's a connection you simply have no capacity to understand. (For instance, when asked to open a thread about what sorts of evidence would support propositions about the supernatural, you opened a thread that was nothing but a list of people who didn't believe you had presented evidence. When it was pointed out to you that that's not the same thing, you made accusations of oppression and fled.) That's because you're not a person who arrives at positions based on the evidence; you're a person who arrives at a position on the basis of what the other people in your tribe seem to think.
Prediction: you'll respond to this post by accusing me of oppressing you in some way.