There's a saying in a negative situation which is usually offered up by a loved one in the intention of solace or hope, "the grass is always greener on the other side." We have all experienced this feeling of finally obtaining what we yearned for only to find that it wasn't what we imagined it to be. It's a terrible and hopeless feeling after wanting something for so long. Yet, continuing the cycle, another dream surfaces and now there is a whole new patch of grass to spy on. It becomes clear that these are all just fields of dreams. Ultimately, you yearn or morn the loss of something you only imagined to be true. How powerful the mind; how fickle.
I'm not too sure if it's actually greener on the other side. I could be wrong though; I've never been able to get onto that field.