"Men do not know how that which is drawn in different directions harmonises with itself. The harmonious structure of the world depends upon opposite tension like that of the bow and the lyre."
-Heraclitus, 475 BCE
"What opposes unites, and the finest attunement stems from things bearing in opposite directions, and all things come about by strife."
The harmony of opposites is an ideal in both taoism's shen and kwei, and in western alchemy, as well as coming up here in Heraclitus, the first greek philosopher. Actually, Heraclitus has a lot of taoist ideas in his writings- change is constant, opposites find unity in balance with each other, etc. Hegel uses the same idea in the dialectic- thesis, antithesis and synthesis. And Jung uses alchemal ideas in his picture of spiritual wholeness, which is both male and female. Derrida talks about words being elusive because of this slippery relationship with their opposite.
I talk about these things here not because I want to show off what I know, but because this is something I don't know. It's something I've tried to understand. This idea that opposites form some sort of balance eludes me- I try to understand how kindness harmonizes with cruelty, for example, and I can't do it. The classic example is night, which when it reaches the point of total darkness starts to become day. This is a bit easier to understand. But, the idea that death and life form a balance is difficult for me to accept or understand.
Education is humbling in this way- every time you learn one thing, along with it you discover three other things you don't know. At this point, I have learned thousands of things that I don't know. By the time I am out of grad school, I expect there will be millions of things I don't know. If I am ever old and wise, there will be billions of things I don't know.