And it slips through our fingers

[Lathriel]

It always saddened me when I read the last few chapters of LOTR and came to realize that magic is truly leaving ME and the decay of many glorious things and places.
But I think this is exactly what life is about. Things can't always continue to be great and there are many examples in history.
To take an obvious example, The Roman Empire, it was great but it didn't last. However, something else will replace that which was lost. The renaisance (although it took some time) again helped the nations flourish. So it is only natural that certain things diminish. That is why LOTR can almost be seen as a historical book. It is because it stays true to these certain realities.