You can prove it to yourself based upon questioning the flat earth "map":
1. What is the flight time from Miami to Tokyo? compare that to the flight time from Santiago Chile to Brisbane. They are both 15 hours. That is not possible on a flat earth because Santiago to Brisbane is 3X as far.
2. A person with his back to the "north pole" standing on the tip of South America , the tip of Africa, and the tip New Zealand will all see the exact same cluster of stars in the center of the souther sky. Not possible on the flat earth model.
3. Where does the sun go? If the sun circles abover the earth, why do I see it set? Not possible on a flat earth.
4. Why does a person standing in Ohio looking across to Toronoto see it's tallest buildings half submerged?
5. Why can't I see Mount Everest from the top of Mount Evans?
6. If the moon circles above us, why can't anybody ever see the other sides of it based upon their vantage? That's not possible based upon the flat earth model.