All our lives we have learned what we think and what we believe to be "the truth".  We've heard things like Bill Gates being the richest man in the world, the Earth being the third planet from the sun, and for a considerable amount of us, that there is a god or greater force, and that we will die.  But there are also a number of things that we have learned by experience, we have two hands, if we jump we will come back down, if we get cut we will hurt.  But the thing is how do we know these things are true?  Because someone told us so?  Because we think that's what will happen because of experience?  How do we know that'll stay the same?  "Because of the laws of physics!" someone will say.  "Because it always has!" someone else will say.  But what makes the laws of physics so unbreakable?  Because they stayed the same before?  Just because you flip a coin 5 times and it's heads all 5 times does that mean it will be heads again?