I'm sure flat-earthers believe, trust, and use many things they cannot see or even understand. Phone, the Internet, TV, their car, etc. etc. They are just doing it because of:
a) a spectacular failure in education
b) religious and political brain-washing that teaches people not to think
c) social outcasts desperate to fit in with some in-crowd
d) pure laziness
e) rampant sport trolling by the bored, lazy, and childish
I'm sure the list goes on - add your own below.
RE: No, Getting on a plane doesn't prove the earth is round. Try again, Round-earthers!