Haven't we all heard the phrase, "Is the glass half full or half empty?" My response used to go like this, "It depends. Did the glass start out full - and then you drank half, or did you only fill it up half way?"
Let me give you a Biblical example: The Israelite's were freed from the bondage of slavery in Egypt (glass half full). They came to the end of the road and found themselves in a bind - angry Egyptians on one side, and the tumultuous Red Sea on the other side (glass half empty). At this point they were faced with a decision: Do we get depressed and just surrender, or do we have faith in God? They chose a glass half full by having faith in God as their deliverer. The result: He parted the Red Sea and they walked across on dry ground.
It's our ability to have faith in God and in His promises that can turn ANY situation into a glass half full.