Sky is the limit

I was thinking over this proverb. Well, I know the meaning of it and I know it has nothing to do with sky or something but it is about the highest level people are able to reach. At least that is how I get this proverb. I may be wrong about meaning and you may bring some corrections into it though it is not the meaning I wonder about but about image. People use image of sky in order to show that sky is the greatest limit and they were wrong when have chosen this image. They were wrong because there is no limit of the sky and there is no sky. I mean, what is sky? Do you know what sky is? I don’t and I know that there is space behind sky though I don’t know when sky is over and space starts. I don’t know where this point is and if there is such a point. Space is something we have above us and at the same time it is something we have around us. There are no limits and no boundaries and no points and no other stuff that may identify some material point of space. Space is the hugest something of this world and at the same time there is no space because we can’t tough it or feel it or smell it.