Why Are We Always Longing For Something More?

Why are we always longing for something more? I think C.S. Lewis puts it well here.

"We talk about a universal experience as with surprise. Why is that? We look at somebody and say, my how you've grown or we say, my how time flies. That would be as strange as a fish complaining about how wet the water is.

Unless of course it was meant to live on dry land."

To go along with that one, from 2 Corinthians 5

"1Now we know that if the earthly tent we live in is destroyed, we have a building from God, an eternal house in heaven, not built by human hands. 2Meanwhile we groan, longing to be clothed with our heavenly dwelling, 3because when we are clothed, we will not be found naked. 4For while we are in this tent, we groan and are burdened, because we do not wish to be unclothed but to be clothed with our heavenly dwelling, so that what is mortal may be swallowed up by life. 5Now it is God who has made us for this very purpose and has given us the Spirit as a deposit, guaranteeing what is to come."