The fact that the horizon remains as far away as it is, not further or nearer however much you may travel toward it should suggest, at least, to our own senses and reasoning that the Earth may not actually be quite as flat as it seems. :nono:
That the Earth, is indeed like the sphere of the moon that those who are not blind can see in all of its phases.
That the tides are still due to the gravitational pull of the moon, even when it is below the horizon.
Of course if you only ever stayed in one place, and never took on board other information, it may not be obvious and take some convincing that this apparent "flatness" does really only apply to the local context and that our unassisted senses don't function as well beyond it.
Should we then stick to only what we can personally experience or do we try to discern evidence from beyond our own locality and sensory perceptions?
If there were any reason for NASA to mislead us then they seem to have done so with the complete assistance of all the nations who put hardware and humans in space, including those from all around the world who spend long periods of time on the International Space Station.
So, what appears to be initially true to our rather limited localised individual human senses soon becomes overwhelmed with all kinds of information from countless different independent sources.
Should we then insist, before being reasonably convinced that all may not be quite as flat as it initially appears to be, that we will simply reject everything unless confirmed by our own perhaps limited senses?