Is the glass half empty or half full? Well, if you're anything like the average American, then chances are you're biased toward optimism.
Here's an interesting article by Tali Sharot of TIME Magazine about science of optimism, and how may just be hardwired by evolution into our brain as a survival mechanism against the knowledge of certain death:
To think positively about our prospects, we must first be able to imagine ourselves in the future. Optimism starts with what may be the most extraordinary of human talents: mental time travel, the ability to move back and forth through time and space in one's mind. Although most of us take this ability for granted, our capacity to envision a different time and place is in fact critical to our survival.
It is easy to see why cognitive time travel was naturally selected for over the course of evolution. It allows us to plan ahead, to save food and resources for times of scarcity and to endure hard work in anticipation of a future reward. It also lets us forecast how our current behavior may influence future generations. If we were not able to picture the world in a hundred years or more, would we be concerned with global warming? Would we attempt to live healthily? Would we have children?
While mental time travel has clear survival advantages, conscious foresight came to humans at an enormous price — the understanding that somewhere in the future, death awaits. Ajit Varki, a biologist at the University of California, San Diego, argues that the awareness of mortality on its own would have led evolution to a dead end. The despair would have interfered with our daily function, bringing the activities needed for survival to a stop. The only way conscious mental time travel could have arisen over the course of evolution is if it emerged together with irrational optimism. Knowledge of death had to emerge side by side with the persistent ability to picture a bright future.
Link (Image: Noma Bar)
In other words, neither is required and transcendence of duality may work out to be the most "evolutionarily advantageous".