What does the initial fragment of The Hitchhiker's Guide to the Galaxy mean?

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?

No, the line didn't say that 'people were concerned about (for) money'. It said that the solutions advanced to solve people's unhappiness concerned money. In other words, the author is making the comment that the suggestions did not address people directly, but were centred on money, as though money, if properly manipulated, would make people happy.

So, it's the people who're unhappy, but it's money that's receiving the attention, even though money isn't the unhappy party.

So, perhaps the suggestions the author is talking about run along the lines of buying stuff, or becoming more financially secure, etc. Financial gain is being addressed, but not the roots of people's unhappiness.

There's an ancient caveat which says that if you have to explain a joke, it isn't funny. The point is, if you don't grasp all the cultural underpinnings being spun around in surprising ways by the joke, you won't be taken by surprise, and surprise is generally the essence of humor. Once you go through the explanation, there's no surprise left.

This statement you are wishing to understand is a joke, pure and simple. It is not something that requires any particular explanation. It's just silliness, just an absurdity. You see, by describing money in an unusual way (small green pieces of paper) Adams catches us off guard. He then says that solutions for happiness often involve money, but he uses the new, unusual term, and then he can say, as if the person making the statement really didn't understand WHY you would talk about small green pieces of paper as a solution to unhappiness, that the pieces of paper aren't unhappy! Isn't it strange to talk about them, if they aren't the unhappy things??

You see how much explanation it takes to make it understood? And you see how it becomes unfunny?

Umm... it's just a joke. :)

(Oh, and by the way, there are other angles on the nature of the humor, but I think this gives you a pretty good idea of how it works. ;)

I guess he meant that instead of dealing with peoples' unhappiness directly by doing something by the people for the people themselves, most solutions involve moving money around.

The focus shifts from moving humans to moving money. We become remote from the ones we help by inserting the intermediate agent between us, thus lowering the level of personal involvement, whereas sometimes it's the exact thing that is needed to make people happier.

Like.. Sometimes a busy father will spend more time earning more money to give it to his children, whereas they may be much happier if he gave them more of his care and his company, not the latest iPhone model.