The reason I said "I believe there is no knowledge" is because all knowledge is based on perception. I perceive that the keyboard under my fingers is black and that the milk on my desk has gone off, but does this mean that those things are true? Others might perceive them in the same way but that does not mean that everyone will: someone with a taste for sour milk might perceive mine as merely well-curdled. I believe that the milk is rotten. They believe it is fine.