I agree with gekko513: the analogy sucks.
If you say it's half full, clearly you consider "full" to be optimal, so it's only halfway there, and you're being way too bitchy because, hey, at least you've got something, so quit complaining.
If you say it's half empty, then, clearly, you're focusing on the part you can't drink instead of on the beverage itself, and so, while you might or might not be optimistic or pessimistic, you tend to look at the wrong things.
And, regardless of half full or half empty, you're way too anal because you've clearly spent time deciding upon the level at which the glass has exactly half of its available volume filled with liquid - no easy feat with a non-cylindrical glass - and you've waited until that exact moment to say something. Loser.
That, or you just don't really care at all where the halfway mark is, and you're just saying something to the effect of "hey, there seems to be something in the glass, because it's neither full nor empty" which is almost completely useless, unless it's of some importance that the glass is either utterly devoid of moisture or is filled to absolute capacity, which is very difficult to do - usually at least a few more molecules will fit.
To me, an optimist is someone who buys a Rev A Mac, assuming it'll all be fine, and a pessimist is someone who already knows that the next round of Macs will have crappy graphics and ship with way too little standard RAM.
No, wait, that's the optimist/realist difference.
