Glass half full vs half empty?

Why is 'glass half empty' considered negative?
And 'glass half full' considered positive?

To me, it should be the other way around!

Half full implies it was empty to begin with.
Half empty implies it was full...

If a waitress handed me a glass, half full, immediate negative feelings arise.
If a waitress handed me a full glass & I drank half, then I'm satisfied & don't need more yet.

Where did this backwards thinking come from?
And why do employers routinely use this question in an interview?
Are they looking for people who will be perfectly happy with half full?

?2013-05-31T03:46:07Z

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Great thinking.
I think when there is a glass half full,people think that it IS half full in the present(an addition of water after it was empty) and if the people think that it is half empty(a loss of water after it was filled)
Employers probably use this question in an interview to see what way you see the situation.
They want to see if you are one who sees the bright side of the situation(optimist) or if you are one who expects the worst in the situation(pessimist).Research had shown that optimists are more successful entrepreneurs,and more likely to be promoted than pessimists.Optimists can also make more money.

?2013-05-31T03:31:46Z

Hmmm, how very philosophical.
Yeah the whole glass half full/half empty thing is so stupid. Like that is the best way to determine if someone is positive or negative.
Also I've never been to an interview before, do they really ask you that question?

Todd2013-05-31T03:54:17Z

Half full suggests it has the potential to be more full. Half empty suggests that it has nowhere to go but down. Pretty simple really. I'm sure most any grade school kid could understand the connection in that form, and not in the way you suggest. Half empty implies a loss, half full a gain or rise from emptiness.