I like a universe where much is unknown and, at the same time, much is knowable. A universe in which everything is known would be static and dull.– Carl Sagan
In a conventional sense, we know some things about the world and the universe and there is a lot we don’t know. We don’t even know how much we don’t know. There may even be many things we don’t know that would turn our whole worldview inside-out and upside-down if we knew them.
Looking a little closer, we see that we don’t know anything for certain. Our brain constructs our perception of the world from our senses and with an overlay of mental images and other thoughts to make sense of it. It’s all constructed. Our perceptions and ideas about the world are not the final word on anything. It’s all created to help us orient and navigate in the world. It has nothing to do with any final truth.
So in a conventional sense, we know a little and we know there is a lot we don’t know. And looking closer, we see that we cannot know anything for certain. Not even that which seems most basic, obvious, and what we take the most for granted.