I did an interesting thought experiment recently. I imagined being the only human on earth, with no pre-existing science or math or historical knowledge or record, but otherwise with the same mental capacity I have now [insert self-deprecating joke here].
For the purposes of the thought experiment, I would not have to worry that much about survival. I would just live my life with relative ease and plenty of time to wonder and think.
I wondered if I would think that the earth was flat. I'm sure it wouldn't be one of the first questions to come to mind.
As I thought more about it, I realized that a more immediate error might be likely. Would I even think there was an 'end' to any part of the world? Why wouldn't I think that it went on forever in any or every direction? I would likely not figure it out through travel, and developing the math and science procedures to figure it out without prior knowledge would not be likely (unless I was immortal maybe).
It probably wouldn't be my main concern, but I'm convinced that I might just assume the earth keeps going.
Unless there is a default setting in the human mind for the finite nature of its environment. I don't know of a time in history where the earth was presumed to be endless. Does anyone else? It could just be that by the time we achieved civilization and record-keeping, the bounds of the earth had been determined, even if only in theory.
I'm sure others would figure it out much faster than I would. But my honest assessment is that I don't think I would discover this on my own if I lived a normal adult lifetime by myself. Maybe there's something I'm missing now that would be obvious to me in this scenario. Or a need that would drive me to its discovery. I'm not sure.