Depends on your standards for "truth". We can never be 100% sure that the Earth isn't in fact flat after all (and everything we measure/perceive is explained by

Depends on your standards for "truth". We can never be 100% sure that the Earth isn't in fact flat after all (and everything we measure/perceive is explained by mass delusion, for example), but we can certain enough that for all practical purposes there's no reason not to assume it's not true.