I'm not sure the shape of the earth is good example here, because I, as someone not doing any geodesy professionally or at all, can accept the "sphere" as such

I'm not sure the shape of the earth is good example here, because I, as someone not doing any geodesy professionally or at all, can accept the "sphere" as such a good enough approximation, like probably millions do. Every model you've seen at school, or in books, or planetariums are (to the human eye) indistinguishable from a sphere, which makes this very much a "well, actually". Yes, I guess after elementary school you'd add some "it's nearly a sphere" and "perfect spheres don't usually exist in the real world", but for all intents and purposes, it looks like a sphere. So maybe it's a good example after all ;)