As I thought over my post on Friday, and the half-full, half-empty scenario that I painted for you, I realized that there was another way to explain it, one that might be more beneficial.
If you are as I am a huge J.R.R. Tolkien fan, you will no doubt know who Gollum is. Well, in the explanation of who he was before he became Gollum is the story of Smeagol, and his sad downfall.
That, too, is a cup half-full/half-empty sort of storytelling.
Smeagol was a fine chap, full of laughter, light and life, until the ring darkened his soul. He was a cup half-full person. Saw the positive side of life. Then, once the ring became his companion, he lost that joy for life. He began to become a negative person, always seeing others as potential targets for killing, especially if they threatened his "precious".
Just another way to look at this building of a character through their viewpoint on the matter of life and situations.
Hope it helps!