It
is a made up number. So what? It's not made up out of thin air though. I should expect to be wrong about 1% of the time when I make such a prediction (and if I'm not it's because I was over or under confident, and should adjust my confidence accordingly.)
So where did the prediction itself come from? My brain, obviously. And that's not a bad thing. Humans are generally good at estimating probabilities. It is essentially what the brain evolved to do. This isn't unique to humans though, there are computer algorithms which can do similar tasks, and mathematical formalizations for calculating certainty.
You can and should be able to assign a probability estimate to anything. When you open your garage door you should expect not to see a dragon. You should be very certain that you won't, actually.
You can't not have any degree of certainty about something. You can expect something to happen. You can expect something not to happen. You can be slightly certain that something will happen. You can be moderately certain. You can think it might have just as good a chance as happening as it does of not happening.
But you can't have no idea what so ever how likely it is to happen. You have to have some expectation of how likely an event is to happen, you can't have no expectation at all.
There is no such thing as a "separate realm" where ideas can't have any certainty values of how likely they are to be true.
As for moving the goal post, religion has moved the goal post plenty. From perfectly testable predictions, to less testable claims, to claims that can't be tested at all.
If you are upset that I, personally, moved the goal post, then just pretend that it was my ancestors that claimed there was a dragon in my garage, and my grandparents decided it was invisible, and my parents decided that it was impermeable to flour, and now I believe that it is a completely untestable dragon, and have decided that dragons are not a matter that is testable by science, and that I've been completely consistent with this belief.