The pessimist sees the glass half empty; the optimist sees the glass half full. Who is right?

Two halves make a whole. The realist would agree that the glass is both half empty and half full. Hence, the pessimist and optimist are both ‘right.’ The difference lies in what they pay attention to.
Should we focus on the good or the bad in people, the bright side or the dark side of a situation, the cloud or its silver lining?
Philosophizing might satisfy one’s intellectual hunger, but not quench one’s physical thirst.
Be it half empty or half full, the pragmatist would simply drink and refill the glass.
“It is astonishing to see how many philosophical disputes collapse into insignificance the moment you subject them to this simple test of tracing a concrete consequence.”
~ William James, Pragmatism