Pessimism, from the Latin word pessimus (worst), is a state of mind in which one perceives life negatively. Value judgments may vary dramatically between individuals, even when judgments of fact are undisputed. The most common example of this phenomenon is the "Is the glass half empty or half full?
Is the glass half empty or half full?
Is the glass half empty or half full? is a common expression, used rhetorically to indicate that a particular situation could be a cause for optimism or pessimism ; or as a general litmus test to simply determine an individual's worldview...

" situation. The degree in which situations like these are evaluated as something good or something bad can be described in terms of one's optimism
The Oxford English Dictionary defines optimism as having "hopefulness and confidence about the future or successful outcome of something; a tendency to take a favourable or hopeful view." The word is originally derived from the Latin optimum, meaning "best." Being optimistic, in the typical sense...

 or pessimism respectively.