a rich person is going to see the glass half empty, because they are used to have someone hired to keep the glass filled constantly.

I am going to see it half full, even if I am not optimistic. Because if I haven't eaten today, and I am starting to think... well ok... I can't eat today, but it is ok, my optimistic side kicks in and says, maybe we don't need to eat every single day and can be a good thing. But hey! Look at that glass almost full !

So... It depends on the observer. Like in the quantum world. What truly happens is that the glass is both half full and and half empty at the same time ;)