How much do you know for sure?

How many unique facts could you swear by?

For me, the answer is none.

There are no facts.

Here's why:
This is how we prove things. We look at a theory, and make it a fact, when we are sure it applies in all relevant locations. Our knowledge, our as in humanity, is facts built on facts. We laid out some simple rules, and explored their implications. Any new piece of information is made a fact as soon as it complies with other facts. What if one of these 'fundamental facts' are wrong'? Wouldn't that destroy everything that we've built on the basis of that? That's where axioms come in.