In our education, we are taught that the Earth is a sphere because it is really a sphere. It would be wrong if our educational system were to teach us that the Earth is flat.
Flat-Earthers claim we know Earth is a sphere from years of propaganda in our educational system. In reality, it is precisely how they themselves can believe something that can be easily shown wrong, like a flat Earth, except that it did not need years to deceive them.
In flat Earth propaganda and indoctrination, the false claim that Earth is flat is repeatedly stated and treated as true. There are plenty of emotional appeals to shield the subjects from reality. They attempt to manipulate us to avoid being exposed to real-world evidence that goes against the claim and to reject them.
On the other hand, in our educational system, we are taught that Earth is a sphere because it is, in fact, a sphere. The fact can be easily verified from personal observation, and our education fully encourages it. Unlike flat-Earth indoctrination, our education does not involve emotional appeals to keep us from reality.
Flat-Earthers cannot distinguish education from indoctrination & propaganda, and they purposefully blur the distinction to confuse their potential victims. However, it is easy to know which one from our education or flat-Earthers tells us the truth: we can observe nature ourselves. We provide several easy-to-perform observations in the category “Easy Observation and Experiments” that we can do to verify that Earth is indeed a sphere.