What can we actually say that we know, as a fact? We cannot know things for certain from a "second hand" source, as the information may be skewed in its transferral. So what we would only know for certain is what we experience. But can we not be deceived by our eyes and our ears? Our senses are flawed in themselves, we cannot hear everything correctly or see everything perfectly. Even when we do we usually distort it with our own perspective, our own judgement.
It amazes me how well everything works in the world despite this chance of being mistaken.