There's this cool thing called science. Millions devote their lives to it all over the world from all cultures and countries. Thousands of years ago early scientists noticed evidence that they didn't live on a flat earth, e.g. different angle of the sun, different stars when they reached the southern hemisphere. We have used that knowledge to explore our world and beyond. The spherical (okay, not a perfect sphere) model is used to model weather, ocean currents and navigation. It works very well. I've been to the other side of the world and I know what jet lag feels like.

If you are happy ignoring all this then it probably makes no difference to your life and I wish you all the best.

BTW some friends of mine who work on space technology will be really miffed that all their efforts are wasted.