I can't believe no one defines this word, but perhaps that's because it's Greek and rarely encountered. A regular google search reveals more for those interested. Think of it as a sort of alchemical transformation:
Jung often referred to Heraclitus’ idea of enantiadromia, the Greek word meaning, everything changes into its opposite. According to Jung, the human psyche itself is comprised of opposites. For example, the word he liked to use to define the male psyche is the Greek word for soul, anima. This, however, is the feminine form of the word. He used the masculine version of the same word, animus, to describe the female psyche. For Jung, the inside of a male is female, and the inside of a female is male. The law of enantiadromia maintains that we all change into our opposites, that men will feminize and women will masculinize.
My friend Paul first introduced the concept to me, so props to him. I think we were talking about how the far left and the far right in politics exhibit a lot more similarities than they'd ever like to admit.
I also found this completely unrelated but rather funny story at edromia.com while researching the word.
This concept is brilliantly depicted in the Taoist symbol of "yin-yang" (click here for a visual depiction). The "eyes" of the contrasting yin and yang complements represent the seed of its opposite whereby it "sees". Imagine that each eye expands until its color fills the containing yin or yang figure while a new eye, of contrasting color, emanates in the center of a new eye, and the whole process iterates indefinitely. Edit (6/2016) This comment placed under enantiodromia.
Yes, the yin-yang is exactly what I think of also. I've spent some years pondering the idea and looking for other examples.
The "modern primitives" have been rediscovering the age-old practices that use pain as a pathway to transcendent/blissful states (such as the Ball Dance from the East where metal balls are sewn into the flesh and then participants engage in vigorous dancing).
There's crossover from the modern primitives into the world of BDSM where this principle is even starker: pain turns into sexual pleasure, restraint becomes release, embarrassment become excitement, etc.
This Sex Magic Primer talks a little more of this in more tantric terms but the principle is there nonetheless.