Let say you see the glass right in front of you, with the water level at half. When you look at things "half-empty", that gives a pessimistic view of things. But if you look at things and think its "half-full", you're looking at the brighter side, mate.
When people refer to the reference as their glass being half full or half empty some people see their glass as half full, meaning that theirs my usually be empty. As I think of the meaning I refer to my glass being half empty. Meaning my glass is usually full, but I might be having a bad day and it would be half empty
