In response to the often asked question of whether the glass is half full or half empty.
Firstly, it has nothing directly to do with Optimism or Pessimism, it could easily be said that the whole question is meaningless without some extra information describing the context. This context is of course in relation to the observer and the object in question, that is, the glass with liquid contents. So taken that your relationship is to fill the glass then the proposed state at 50% would be half full, if the context however is to empty the glass then the state is of course half full. This is because the state has progressed from being full to half-empty, en-route to empty, this shows your progress in a positive way in both cases indicating that a real-time change is in progress.
There is a question arguing this asking how this applies when the observer has no relation to the glass, that is, there is no interaction. The answer to this is that the question then becomes irrelevant. The glass is then in effect not yours and therefore stop worrying about the volume of Guinness in other peoples pints, unless of course you are buying a round.
I am fed up of people saying that I am pessimistic when in actual fact all I am doing is just sending my glass into an empty state.