Inevitability of change and loss

Ok so i just read The Catcher in the Rye and was looking up some themes and ideas from the books when i ran accross a theme of the inevitability of change and loss thats haunts the main character. I thought this idea was interesting.

There are many sayings to cover this but what it seems like to me is us humans desire things far more when we can't have them anymore then we we had them. You don't appreciate what you have until you don't have it anymore. When we lose something or somethings changes and we can't go back to the way things were and there is nothing we can do about that, we always want things to go back to the way they were. When we have something in our head, it is hard to get rid of the idea especially when we want something and we cannot get it back. In essence, the various items, people, times, ect. that might change or have been lost might not actually be all to negative maybe even positive but when we know that there isn't a possiblity of turning time back and having what we had, we get into a state in which we think that what we had before was somehow better than what we have now. This is because it seems like to me that we desire things that we can have or did have far more than what we do have despite the circumstances. Everything seems more tempting when we can't have it. What hurts us the most is that the chnage or loss is inevitable. I jus think this is a flaw in our make-up and can really cause some issues. What bothers me about this is that these changes might even be for the better when you break things down yet we still long to have what we had.