You want to understand something you are completely in the dark about. Where do you start from?
Finding two mutually exclusive and exhaustive states is the oldest and most powerful resource you have. For many millenia, in order to know beyond what we could immediately see, we framed questions against stories with two characters.
Any pair of states defined and set off against one another, like light/dark or hot/cold, is a good example.
Literature is dominated by moral dilemmas faced by individuals in front of dual archetypes such as good and evil. The dynamic between a protagonist and antagonist is what makes every story memorable. It's not a coincidence that "going from Zero to One" has become a Silicon Valley mantra.
Think Harry Potter and Voldemort, Frodo and Gollum, Achab and the White Whale. Dualities represent two sides of every struggle. It's Yin and Yang in Chinese philosophy. Their conflict and interplay is central to an overarching narrative evolution.
Binary phenomena are not just clear-cut, either-or situations. They are worlds building blocks that can be assembled to bridge the messages of different stories. A simple ordered set of states - "How much happiness are you feeling from 1 to 10?" - allows us to speak about gradual change in intersubjective perceptions.
Duality refers to a situation where two related structures can be transformed into each other. Dual concepts are ultimately two ways of speaking about the same thing. In economics most of the concepts used are dual: supply-demand, production-consumption. In mathematics and formal logic, duality principles are everywhere.
From Boolean Logic (where results holds if your switch every and with or and every True with False), to Set and Order theory (where you get a notion of something self-dual), or crucially to Projective Geometry, which is made possible by a dualising statement: "two points are on a unique line and two lines meet at a unique point".
Stories of two characters are the first principle of interplay in an open system. They break up chaos and create symmetric relationships.
Until the next cloud,
David