At any rate, I think the lyrics to the whole song (aka, "They Paved Paradise") sum up the idea quite well, which is that you can't properly appreciate all of the good things you have in life until you have to live without them. If you're curious, here they are:
Joni Mitchell - Big Yellow Taxi Lyrics
A version of the saying that I am quite familiar with, and that expresses the same idea, runs, "Never missed the water till the well ran dry."
- For Teachers