Actually Rov the idea that people though the world was flat is a bit of an urban myth.
A few Early greeks thought that but at the same time one ( Eratosthenes ) knew enough to measure the diameter of the Earth and get it right to within about 10%
Seafarers knew the earth was round as they could see the masts of ships over the horizon and later could calculate lattitude.
This is an interesting theory, but it's very new. It has yet to show that it is at least as good as existing theories, that it can explain what we see as well as they do before offering alternative explanations.
A bit of a case of running before you can walk.
As fot the <Spooky voice> mysteries of the Universe <\Spooky voice> It's obvious we'll never understand everything but it's amazing how much we already can and do understand.
That knowledge really is one of the crowning achievements of our civilisation - which is why we mustn't stop probing and extending that knowledge, there's still so much more we can learn.