Glass is half full?

At dinner tonight with our kids, Erin was explaining the glass is half full/half empty concept, when R___ tells us she can’t answer the question without knowing the context. “If I am filling the glass when you ask me, I will say it is half full, because I’m halfway done with filling it. But if I am drinking the glass when you ask, I will say it is half empty, because I’m halfway done with drinking it.”

I wish I had the perspective of a eight-year-old.