Have you ever noticed that the horizon doesn’t seem to fall? It is always at eye level. Even when you are on an airplane. Flat Earthers have noticed:
2) The horizon always rises to the eye level of the observer as altitude is gained, so you never have to look down to see it. If Earth were in fact a globe, no matter how large, as you ascended the horizon would stay fixed and the observer / camera would have to tilt looking down further and further to see it.
I see it as proof of one thing only. No flat Earther has gone far enough away to see the horizon fall below eye level.
Why would a horizon stay at eye level anyway? If the Earth is indeed flat, or even a concave lense, if an observer travels high enough it will eventually appear flat:
This is the same with a flat disc of limited dimensions too. Eventually you have to look down to see the edge:
The horizon only stays level with the eye forever in the case of an infinite plane. For small distances of about 300 miles of viewing radius, the ball Earth actually behaves in just this way.
Eventually, a person can get far enough away from a planet that it will look like a circle, and he will have to look down (toward Earth) to see the horizon. Even if a person does not want to leave the comfort of his back yard or has a fear of flying, there is another way to see what this is like. With a telescope, he can look at any of the other planets (Venus, Mars, Jupiter, and Saturn from Hubble but viewable with a good scope):
Without a scope, a person really needs to get about 8 miles up to start to visibly appreciate the horizon descend (much earlier than it would if the earth were flat).