Why does the grass ALWAYS look greener on the other side?

My grandmother always had a saying about everything, some of them you had probably heard in your life... and others that I am sure she just made up! :) But one that she would always say is "the grass is always greener on the other side". I had heard that one before and I have learned throughout my life that this one really seems to be true, I think everyone feels that way sometime in their life. Why is that? 
(Confession... this is a photo of my yard, Lauren had to do a close up on the grass because most of it is weeds and dandelions so...I needed for this post to at least see SOME grass!  And of course photo shop, helped it look a bit greener.) Ok, back to my point!
It does seem like when we look through or over the fence that ( or on the outside of people's lives ) that things really do look greener (or better).  Why is that?

We know that they have dandelions too, but somehow we only notice how much greener their grass looks than ours ( or how much bigger or better their house is than ours). Is it, that we spend so much time looking at their grass (or LIFE), that we forget to take care of our own? Is it really greener, (or better), or do we have a limited point of view?
For myself, I know that it is how much time I spend focusing on how much more others have, instead of being grateful for what I have. I have to remember too, the old saying "What you see, isn't always what you get!". I think that is a saying, or maybe I just made that one up, but it is true.
How many times have we judged someone of ...having it all, only to look again or closer, and see all the problems they struggle with. Some people are just really good at putting on their Sunday face or Game face, we might NOT always see what is REALLY going on in their lives.
So let's maybe take, less time looking and focusing on the other side, and more time focusing on what we have and taking care of what we have!
Yes, some day I hope that I can show you a beautiful photo of a lush and green landscape in my back yard, that of course would have to be in the future, because it would take a lot more money that we have right now plus a better and stronger back...but I can hope! The good news is...if you were my neighbor, then you would not be coveting my greener yard, but probably feel instantly better about yours! :) See isn't that a positive way to look at life and my yard? :)

" We can never judge the lives of others, because each person knows only their pain and renunciation. It's one thing to feel that you are on the right path, but it's another to think that yours is the only path"  ~ Paulo Coelho

"Good judgment comes from experience, and experience comes from bad judgment."  ~ The Old Farmer's Almanac

"When you judge another, you do not define them, you define yourself."  ~Wayne Dyer