The state of the glass depends on the state that it was in before. If the amount of liquid has increased since the last state, it's half full. If it has decreased, then it's half empty. If there's no way to tell whether the last state held more or less liquid, it can only mean one thing: the glass is broken.
So yeah, I think the glass is broken, which would put me into...what category? Dunno, therefore, it must mean that I'm broken as well.
But I suppose, we could say that I'm somewhere between realist and pessimist.