There are, it has been said, two types of people in the world. There are those who, when presented with a glass that is exactly half full, say: this glass is half full. And then there are those who say: this glass is half empty. The world belongs, however, to those who can look at the glass and say: ‘What’s up with this glass? Excuse me? Excuse me? This is my glass? I don’t think so. My glass was full! And it was a bigger glass!’ And at the other end of the bar the world is full of the other type of person, who has a broken glass, or a glass that has been carelessly knocked over (usually by one of the people calling for a larger glass), or who has no glass at all, because they were at the back of the crowd and had failed to catch the barman’s eye.

Terry Pratchett, The truth