2022-11-15 [updated 2023-03-30]
THE PROVERBIAL GLASS from WIKI
"Is the glass half empty or half full?" is a proverbial phrase, used rhetorically to indicate that a particular situation could be a cause for pessimism (half empty) or optimism (half full), but there are other view points too, like realism (if poured out, half empty; if filled up, half full, but it is only a point of view), or as a litmus test to simply determine an individual's worldview. The purpose of the question is to demonstrate that a situation may be seen in different ways depending on one's point of view.
The question calls for a binary response while the situation is not at all binary. For example, the correct answers are not "Half Full" nor "Half Empty." The correct answers are either "Yes, the glass is half-full or half-empty" or "No, the glass is neither half-full nor half-empty," For one thing, you have to know what is meant by "full." Are we talking about the level at which addinfg a drop overflows the glass, or are we allowing some lesser volume to be designated as full? I own some "12-ounce mugs" and some "12-ounce" Styrofoam cups, and they each and severally accommodate twelve ounces of liquid with a bit of room to spare.
Although you can certainly drink from a measuring cup or a graduated cylinder or even a pipette, people don't routinely do that. (I am not people. I used to drink from a two-cup Pyrex measuring cup all the time, until I broke it.) The point is that unless you measure the amount of water, you're just guessing whether it's half of capacity. It's that guesswork that permits people to ascribe optimistic or pessimistic attitudes. Note that the wiki speaks of vector quantities as well as scalars. If the level is going down to empty, it's halfway there. If going up to full, it's halfway to that goal.
Humor sites will have other points of view. About other POV:
“This is the most important lesson you must learn about magic,” Miss Ochiba went on. “There are many ways of seeing. Each has an element of truth, but none is the whole truth. If you limit yourselves to one way of seeing, one truth, you will limit your power. You will also place limits on the kinds of spells you can cast, as well as their strength. To be a good magician, you must see in many ways. You must be flexible. You must be willing to learn from different sources. And you must always remember that the truths you see are incomplete.” - Wrede, Patricia C.. Thirteenth Child (Frontier Magic Book 1)
I've always though that it doesn't matter whether the glass is half full, half empty, or any other variation. The glass is refillable!