Half Empty? or Half Full?

I have always been pretty fortunate to be able to surround myself with positive people.  I've had a few "Negative Nellies" over the years but more often than not, I've been fortunate to always work with people who were positive.

Over the last couple of years, through necessity more than choice, I've been surrounded by a plethora of glass "half empties" rather than glass "half fulls".  It has made me think a lot about what makes people that way.  It takes so much more energy to be on the "half empty" side.

Does it happen because most negative people tend to focus on what they don't have rather than what they do have?  Why can't people just be positive and thankful for all the things they do have:  health, family, friends, etc...It just seems as though some people are never happy.  And looking at the world through a "half empty" glass affects all of your relationships and everything you do.

How do you see the world, or rather, how do you think others think you see the world?  Are you a "half empty" or "half full" person?  And, is it a "partly cloudy" or "partly sunny" day and is there a difference?