Is the glass half empty or full?

It depends on how you look at it and your perception of things. It is a common expression, used rhetorically to indicate that a particular situation could be a cause for optimism (half full) or pessimism (half empty); or as a general litmus test to simply determine if an individual is an optimist or a pessimist. The purpose of the question is to demonstrate that the situation may be seen in different ways depending on one's point of view and that there may be opportunity in the situation as well as trouble. This idiom is used to explain how people perceive on events and objects. Perception is unique to every individual and is simply one's interpretation of reality

Full...

The glass is full with air and liquid.
Some portion (half )of the glass with liquid or water and the remaining portion with air, so its FULL.

Half empty,half full.......