That was my immediate thought regarding puzzle piece 4. To say “X could happen” is just to say “I am uncertain about X, or I don’t have sufficient information to rule X out”. The impossible (e.g., for me) is what I can rule out; the possible is what I can’t. People talking about what’s really, really possible and impossible are just talking about what they believe the closest-to-perfect (but still imperfect) agent could know.
That was my immediate thought regarding puzzle piece 4. To say “X could happen” is just to say “I am uncertain about X, or I don’t have sufficient information to rule X out”. The impossible (e.g., for me) is what I can rule out; the possible is what I can’t. People talking about what’s really, really possible and impossible are just talking about what they believe the closest-to-perfect (but still imperfect) agent could know.