As the Bible suggests when someone eats the fruit of knowledge, they are thrown into the world. Here, to eat the Fruit of knowledge resembles the activity, behaving in such a way that influences in the vicinity.  Being thrown into the world means gaining the capacity or ability to experience, realize and properly anticipate events, feelings and emotions and one can distinguish between right and wrong, good and bad, and morals of the society

If the Bible is not wrong, we can conclude that for someone to live their life two things are essential: one is action while the other is accountability. Accountability is nexus with the terms ethics and morality. This is the reason why there developed a concept of two worlds: The inner world and the Outer world. 

The outworld is connected with the materialistic aspect whereas is Outer world is with the perceptions that one holds. These two dimensions seem to be conflicting with each other but in-depth they are complementary with one another. 

Here, I would like to include the definition of darkness by Albert Einstein, according to him: "absence of light". The subjects seem opposite to one another but the way of understanding makes them behave as if they are one or entangled to the same thing and differ only in the way of seeing it. This is what holds the Duality.

The concept of Duality holds everywhere.

A baby crawling out of the cradle and marching towards life but as seen from another angle the stop point is the graveyard. Is it to the livelihood or the death? Both ways hold in the equation of life.  So, how to perceive it depends upon us. This is the duality of life. 

The duality of life is not a matter of the seer but it is the characteristics of life.