Is the Grass Always Greener?

Just something I've been thinking about lately.  Is the grass really always greener on the other side?  What about people who always seem to be extremely happy with what they have, who they are with, and where they are in life in general?  How did they get to be that way?  Is this a learned behavior?  If so...how do we teach it? 

Then again...do you really want to teach everyone to be this way?  My guess is...probably not.  This "grass is greener" concept is probably what drives people to move up in their careers or out of bad relationships knowing that they can achieve better/more. 

Should you ever settle for what you've got or should you always be expecting and reaching for more?  Like most things, it seems that it can be helpful in some instances and not helpful in others.  It can't be a good thing to live your life always look for tomorrow or the next best thing to come along. 

SO....How do you know you've reached the best of what you can get?  Does it depend on whether you are talking about work or personal? 

On a related note:  I don't have any regrets in my life (and still don't) because I believe that everything that happens to you has put you exactly where you are today and I can't really complain with my life today (so even the bad things...helped you get to where you are today).  However, very recent events have me thinking about the past and wishing I could go back in time.  Just for fun...just once.  Just to see how things could have been different.  I don't actually want to change anything about today, so if someone actually offered me that opportunity and told me that they couldn't guarantee I would come back exactly to where I am today then I wouldn't do it (it would scare me that I might not end up happy).  But boy...I sure wish I could just go back for one summer back in '8x.