Is the glass half-full or is it half-empty? We have grown up with this question. It is said that an optimist sees the glass half-full, whereas a pessimist sees it otherwise.
However, look at the other way. Instead of just seeing the glass, what would happen if you have to explain about this point on optimism/pessimism to someone? Psychologists have done various experiments on questions similar to this and concluded that the way you present a message can change its interpretation.