What is knowledge? Kind of a weird thing to think about. Because you do know something, while at the same time you don't. Because, can you really know something?

If so, how? How can you be 100% sure of something? Or 90%? Can't there always be things you haven't taking into consideration, or simply do not understand? And if not, how do you know? Who will tell you that you know the truth in a certain matter? That you are right. Someone with more knowledge is more likely to correctly predict what will happen, and therefore deserve proper attention. But they can be wrong. Or can they?