Rocks don't think.

As far as we know...

It's not about intelligence, there are plenty of intelligent people who believe a lot of stupid bullshit. For most Flat Earthers, it's more an issue with their ability and willingness to reason in combination with "objective" self-awareness. Obviously it's impossible to be completely unbiased, but you have to at least want to be. I'd argue that if someone's thinking consistenly leads to demonstrably false conclusions, it's fair to say they're not doing it right.

If the sun is directional, like a flashlight you hold relatively close to the flat disc, you can move it around in a circle say along the inside of the circumference of the disc, then this creates “night” for those portions of the disc outside of its range…

Oddly enough, this might work as a sort of projection to model the actual path of sunlight across a flat projection of a map of the earth.