That's how i've always thought of it.
If you view it as half-empty, you're looking at what's missing from your life as it stands to that point, and perhaps subconsciously want that missing material.
At least that's what I feel this perception test signifies....
Half-full for me.
This shouldn't be taken so literally... if you view it as half-full, you're grateful for what you have and you take what you're given without questioning it.
We simply refuse to commit to a presupposed outlook.
If the glass has snot and puke in it, then it wouldn't necessarily be seen as being a pessimist if its half empty or an optimist if its half full, because that's just gross and nobody wants a half a glass of snot and puke.
If that is the case, then all of you must be henceforth terminated on the spot without the beastliness of forethought.
if you view it as half-full, you're grateful for what you have and you take what you're given without questioning it.