My optimism about Brexit can only have any proof once Brexit has actually happened. I don't need to prove that I am optimistic, I can state it as first hand knowledge.
I'm so sorry that these concepts are so difficult to understand.

That is not difficult in the least to understand. You can be as optimistic as you like, no problem.

However, if you want anyone else to share that optimism, you need to explain the foundations of it to them. Is that difficult to understand?