I also tought about that and the most simple thing is look at this,
I know what 1+1 is YEAH I know something! In the end you don't know why you are calling something 1, even now you can say I know why we are calling it 1, but every time it goes deeper and deeper and the only thing why you think you know something is, because YOUR BRAIN THINKS THAT, YOU DON'T.

ya but then it means we really don't know anything even we work it out.

First we have to define knowledge: if we consider knowledge as the capability to reach the true meaning of everything in the world, then we are damned to absolute ignorance ( we Are bounded to our imagination, to our brain: what do we exactly know about how a tree perceives the world, about how it 'feels' its life?). But when we look at knowledge as comprehension of Human reality and Science as the way man perceives the world, then, maybe, we will be able to take some steps.

What I believe is that we truly dont know anything. Think about all of the mysteries in the world. If we compare that to what the average human knows then you will understand that we know little. All we know is that we are here on this Earth. But for what? There are tons of mysteries surounding, not only us, but everything. What do we actually know and how much of it is actually use full.