The thing you would never do
Answer in your head. Then keep going.
It says you can't know — and neither can anyone. That isn't an accusation, and it isn't a suggestion about your character. You may be exactly the person you think you are. Most people are, most of the time.
It's simply that you have a map of yourself, drawn entirely from the ground you have already walked, and you have been reading it as though it covered the whole country.
Uncertainty is constant change in every unit of change. However fine a unit of change you take, that unit is itself changing. There is no smallest still piece for change to be made of — no still frame anywhere, nothing that holds long enough to be finished with.
So the map doesn't fall short because it's small. It falls short because the territory won't hold still. What I don't know will always exceed what I know. The territory always exceeds the map. Uncertainty is infinite; certainty is always finite.
That's the Null Hypothesis, and everything here starts from it.
It doesn't mean nothing can be known, and it doesn't mean you must understand everything before anything makes sense. That's the panic people fall into on first seeing the floor, and it's wrong.
Certainty is real. It's just finite, and local, and earned — not the ground you start from, but what you're handed for having moved.
You don't discover you're brave by imagining it. You find out the first time you do the difficult thing anyway.
So who exactly is it that would decide, in a moment you have never faced?