Is the glass half-full or half-empty? Or is the glass just twice as big as it needs to be? The point here is that we often see what we want to see. Reality is just a matter of perception. Two people see the exact same thing and both are sincere when they say they see it a certain way, but that way is different. Which one is right and which one is wrong? (Murkin, Lance. "Is the glass half full or half empty." Retreived from: http://www.dreammerchant.net/murkin_apr2000.htm )
whoops!! - I didn't know that article was selling something.
To get to your question, I'm not sure if that phrase really had an origin (prove me wrong someone?) It just seems like one of those phrases that fell into common ideology.