The Thinking Behind The Tweet

Actually, the question should be - 

Is the glass at least both half-full and half-empty?

Rather than limit people to 2 ways of thinking and claiming one is optimistic and the other pessimistic, we ought to encourage people toview Situations and People's actions from multiple perspectives...by, for example, encouraging people to use tools like Edward de Bono's 'Six Thinking Hats'.

In some Situations, it is appropriate to consider what has been added while in others it is appropriate to consider what has been subtracted. Sometimes we need to consider possibilities. Other times we need to identify the need for urgent action. 

This goes beyond optimism, pessimism, and realism. While that 'mindset' differentiation may be important, with people or with situations, it also may not be important.

Situations & People deserve a lot more thinking than optimism/pessimism tests.

PS: That glass-half-full-glass-half-empty saying has always annoyed me. It is too cliché and it puts people into a 2-dimensional box when all of us know we live in at least a 3-dimensional world.