Is the Glass Half Empty or Half Full?

This is an interesting philosophical question.

The typical answer would be that someone with a positive attitude (optimist) will see the glass as half full, while someone with a negative view of life (pessimistic) will see the glass as half empty.

Posed with the questions, in a survey, it is interesting to note that most people want to be seen as optmistic. So can this question tell optimists apart from the pessimists?

Why is it we have the tendency to perceive that it is a negative thing to see a half-empty glass?

Since the glass is half empty, it has the capacity to hold more water. So what are you waiting for?!!! Go fetch more water to fill your glass.