At least I think it is.
Because I have never heard about a ship falling off the end of the ocean.
And there are horizons.
And I have seen photos from space.
But I have never been to space. So, I have to trust that someone has been up there. To accept what I see as true. We all have to rely on experts that the assertion they have made of the world is true.
It’s the same for car mechanics and climate scientists.