I begun reading Douglas Adams' The Hitchhiker's Guide to the Galaxy.
This is one of the initial fragments, emphasis mine:
This planet has - or rather had - a problem, which was this: most of the people on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movements of small green pieces of paper, which is odd because on the whole it wasn't the small green pieces of paper that were unhappy.
I don't quite grasp what he intended to say with this last line.
So, sad people were concerned about money: "which is odd because money wasn't the unhappy one". This doesn't make much sense to me.
What is the meaning of this last line?