How do I know what I know?

I know what I know because it was told to me. Or I discovered it for myself. I know a pan is hot when it has been heated by fire not because someone told me it was, although im sure sometime in my life someone has, but because I touched it. And it was most certainly hot. Other things that I cant possibly discover for myself, such as the earth is round and not just a flat surface in space and if I venture too far off one side, oops, I fall into the abyss that is space, I take on good faith. You have to base what you know on trust. This is true for all aspects of your life, but especially in this one. If you cant trust someone, than most of what you know becomes false. And you degrade into a hermit sitting alone questioning why a chair has four legs instead of three, and no one wants that. If a book that is given to me in school says that the earth is round, I have to take it on good faith to be a true statement. It doesn’t mean I have to believe EVERYTHING I am fed has to be true, you have to be your own judge on the matter. If a man on the street tells me the aliens are coming, I disregard this statement as false. Do I know for a fact they aren’t coming? No, but can I assume the man is crazy? You bet.