Glass half what?

I am perplexed by the commonly used phrase 'the glass half full'?

What is in the glass?

Is the half that is in there a liquid? Would it change the meaning if it wasn't?

Why don't you count the air as something? It's still in there with whatever this other stuff is?

Where did the rest of the alleged liquid go? Did you spill it? Do you need to clean that up?

Did you ignore it for so long that it evaporated?

Can we just do ONE THING to ease my mind and tip it down the sink so we can talk about something else?

#doonethingdeep #wackyexpressions