Look at a calm lake from the shore: the water sits flat and level, and the far bank doesn't visibly curve away. That makes me feel the Earth is more flat than ball-shaped, honestly. My opponent may have fair points, but I don't really know how to argue back beyond that gut feeling.

Stand on a long straight road across flat farmland and the horizon looks level all around, not obviously bending. My opponent makes a fair point and I'm not sure how to argue back, but that still leaves me feeling the Earth is flatter than a ball.

Imagine scanning a wide parking lot or field on a clear day: the ground reads as flat and level, with nothing curved like a ball jumping out. My opponent makes a fair point and I am not sure how to argue back, but my gut still says flatter than a sphere.