Contextualism is the treatment of knowledge as context-sensitive. In discussions about the shape of Earth, flat-Earthers like to use the extreme denialist context in which if there is any tiny possibility that we might be wrong, then we do not know it at all. But if we apply the same context to everyday scenarios, we will fail to function as normal human beings.
To avoid unreasonable arguments, we can shift the context back to what applies to everyday scenarios. If these people ask, “How can you be certain of <something> if you haven’t proven it yourself?” we can reply, “The same way you are certain that North Korea is real.” In an everyday context, we all know North Korea is real although most of us cannot personally prove it.