286. What we believe depends on what we learn. We all believe that it isn’t possible to get to the moon; but there might be people who believe that that is possible and that it sometimes happens. We say: these people do not know a lot that we know. And, let them be never so sure of their belief—they are wrong and we know it.
If we compare our system of knowledge with theirs then theirs is evidently the poorer one by far.
467. I am sitting with a philosopher in the garden; he says again and again “I know that that’s a tree”, pointing to a tree that is near us. Someone else arrives and hears this, and I tell him: “This fellow isn’t insane. We are only doing philosophy.”
Ludwig Wittgenstein, On Certainty