To see the round earth, there is no need to rocket out to space. You can see the earth’s curvature anywhere by looking out to sea, down from a hillside, or across a big flat plain. When you gaze at the sky, everything appears round — the moon, the sun, other planets, distant stars, and even solar and lunar eclipses. What made our early ancestors think that the earth was flat? Why had they failed to see this great truth for so long? Did they possess any common sense at all?
Human history can be traced by the fossil of a skeleton to about 200,000 years old. By the same way, modern civilization is thought to begin around 6000 years ago. The concept of the spherical earth is traced to ancient Greek philosophy around 2600 years old when astronomy also began. Nevertheless, the round-earth concept did not gain popular acceptance until only 500 years ago when Magellan circumnavigated the earth. Why had the flat-earth concept lasted for so long?
Considering human progress from the beginning age of the caveman to the modern scientific exploration of Mars, I think the human mind has much greater capacity than for survival only. It is also able to understand the universe and unlock its secrets, gradually in the ancient era but exponentially in modern times due to the explosion of scientific knowledge. I believe that some tribes of our ancient ancestors had already figured out that the earth was round well before the Greeks 2600 years ago, which is officially known as the beginning of the round-earth concept. Although I cannot prove it, let me give you the reasons why:
First, some tribes somewhere might have carved a spherical earth on a piece of stone waiting to be unearthed, just like a fossil has been unearthed to show that the oldest human form existed about 200,000 years ago. There will always be more secrets to be unearthed later.
Second, communications between different ancient tribes were difficult or non-existent even though they lived close to each other. As a result, the round-earth concept stayed within the isolated tribe for a long time.
Third, tribes were led by a chief or elder who had absolute power. It is human nature that a ruler rules either by physical strength or intellectual power. In ancient times, intellectual power means being able to invent and propagate myths that the rest did not understand but must follow. The empirical round-earth concept ran counter to all ancient myths and so must be rejected or suppressed. The round-earth concept was not important in ancient times because the tribes rarely traveled long distances, thus it was easily suppressed. Other empirical concepts like gravity, the changing seasons, growing crops and domesticating animals were much more important because they related to life and death. Likewise, the positions of the stars were more important for worshipping, navigational and timing purposes.
The suppression of new ideas to preserve the old myths continued for a long time in the feudal societies that developed from the ancient tribes until the Industrial Revolution around 1700 A.D. shook up the entire system. Before that time, people who discovered new things that contradicted with established doctrines were banished as lunatics and even executed for their believing in the truth.
Therefore, my conclusion is that for a truth (big or small) to come out, it must overcome the coverup and suppression imposed by the establishment if it runs counter to their own interest. The establishment may be a government, a religion, a powerful organization or a big private company. In the modern era, although the truth cannot be suppressed by brute force as in the old times, it can easily be covered up by a maze of invented technical details that few people understand (as shown by all the financial scams). Furthermore, a truth can remain hidden for a long time if the public want to be blind followers and do not try to question the status quo.