Half empty

You know how you're supposed to be able to tell if a person is optimistic or pessimistic by whether they think a glass is "half full" or "half empty" ? Well I think that is a load of rubbish. A glass is half empty if it is half way through being drunk. It is half full if it is being filled up. It all depends on which direction the liquid is heading. It also means that a glass is more likely to be half empty than half full, because it's only half full for that moment right in the middle of pouring the glass at the beginning of the drink.