A person in a lab coat places a glass half-filled with a yellow liquid in front of 4 people.
Immediately, the first person pipes up, "Ah, I see the glass is half full!"
This person is an optimist.
The second person states, "Naw man, why would he bring us a half-full glass? He obviously drank some. It's now half empty."
This person is a pessimist.
The third person scoffs, "Why must you two argue? It's just a glass with liquid in it."
This person is a realist.
While the three of them bic…