>But how could you be alive and not have observed that the earth is curved?
I know someone who is almost 40 years old that has never left his hometown. He's a reasonable person who holds gainful employment, but from our conversations, he's never been in a skyscraper, flown on an airplane, taken a road trip into the mountains, or even hiked up a large hill, for that matter. He also lives in a land-locked city, so he's never seen the ocean. As such, he has never directly observed the earth to be curved. With all due respect, many people like him do exist in the world, and perhaps you're not acquainted with people like him.
However, he is not a flat-earther because he spends much time on the Internet reading about the way the world works outside his hometown. Basically, he believes in the truthfulness of large institutions, which really is why you and I believe the earth is round; that is, we haven't actually performed a bona fide experiment (not just going in an airplane or up a mountain) to measure the curvature of the earth for ourselves, but we trust the results of those who have, and we also accept that certain technologies like GPS as it is currently implemented can only work if the earth is round (not just in satellite orbits but also the slight-but-critical relativistic shift from a geosynchronous satellite).
>when the contrary idea takes enormous leaps of faith to consider, it seems weird to me to believe something for the sake of it.
That's cool, but many people are capable of believing in something for the sake of it. One fact that stands out to me is that we all use some amount of faith to accept that the earth is round, though perhaps not quite a leap's worth.
> With all due respect, many people like him do exist in the world, and perhaps you're not acquainted with people like him.
Fair enough.
> Basically, he believes in the truthfulness of large institutions, which really is why you and I believe the earth is round; that is, we haven't actually performed a bona fide experiment
I guess to a certain extent, but also knowing that I could perform such an experiment and come up with reproducible results. As well as the lack of any credible alternative theory that holds up to any sort of scientific rigor.
> One fact that stands out to me is that we all use some amount of faith to accept that the earth is round, though perhaps not quite a leap's worth.
I would say that it's not really faith when its reproducible. For example, there is a small amount of faith that my brakes will slow down my car when approaching a corner, but I can test the brakes to know they should work, I can perform experiments with similar mechanisms to prove the basic physics, that all would have reproducible outcomes. So while there is a small amount of faith that some catastrophic failure won't happen, I would say its categorically different to believing things with almost no evidence. There is no reproducible experiment (at least that I know of) that you can even read about that proves the earth is flat.