This example is taken from The Atheist Experience #814, the bag of dice example of possibilities: Let's say I have a bag. You can't see what I have in the bag. There's nothing uncommon about this bag. I ask you if I can roll a 21 with the dice that I have in my bag. You say, "It's possible". I then open my bag to reveal that I have one normal, six sided die,which has one number on each side, numbering 1 through 6. Is it possible to roll a 21 with this die? No. So, it was not possible to roll a 21, but you have already declared something possible that was, in fact, impossible. Wouldn't it have been more correct to say that without knowing what's in the bag (one die, several dice ... no dice), that we don't have enough information to make a declaration one way or another?
For me, this is the problem when we say that we know for a fact things that we have not been able to confirm with objective evidence. Word of mouth, ancient stories, or finding coincidence, isn't enough information to make a declaration that we know for a fact that there is anything beyond the physical world. Is it possible that there is? Just like with the dice, I don't have enough information.