Whether the interdependence of opposites is observed in negation, Yin Yang, ecological balances, God Vs. Atheism, pop-culture's "The Balance in the Force" from Star Wars and so forth I think there's a third aspect that goes unaccounted for which coincides with some of Hegel's theories on the "synthesis."

For a more specific example of complimentary opposites let's look at the Yin and Yang. Although the duality is existent, observable and at times reliant, my problem lies in the very fact that it is observable. As a result of acquiring this observation of a "Yin Yang" system we are also acquiring knowledge.

For example: A baby observes daylight (since day is the only thing he's seen he's unaware of its presence/absence). Then he observes night and realizes that daylight is not constant or a law and that by it can be absent, therefore through negation he defines daylight and night.

Here the baby has acquired two complimentary sets of knowledge by observing: day and night. Yin and Yang, from my understanding, stops here and says one can't exist without the other and that the baby should always look for these interdependencies of opposites.

Now I'd like to provide a second example that may show how a third element to the observance of Yin Yang (or the interdependency of opposites) may become present: A child realizes that they can't always be happy. Without sadness one can't find themselves appreciating happiness and vice versa. Therefore to be happy one must have experiences of sadness at times.

At this point, the Yin and Yang has been discovered. However, this is where I believe a third element to this equation has arrived. By realizing that one must be sad in order to be happy one has acquired the knowledge of a certain key to being happy. One can now be more positive and optimistic the next time sadness enters the person life since they know the end result is more gratitude for happiness later. Why do we not fear the rain and thunder anymore? Because we know that sun will arrive later. Similarly, why do we not do wish rain whenever there is too much sun? Because we know that the rain will arrive eventually. Thus, the sadness and aggression associated with rain-wish is removed by an optimistic outlook.

Let's suppose we avoided this third element I've proposed. We do know that happiness will come after the sadness, but choose to only look at the Yin Yang aspect that it will be balanced out. By doing so, it would mean that when the exact opposite emotion occurs (that we're happy) then we'll focus on the fact that we're doomed to eventually be sad again. However, my proposed third element would say that it's the knowledge of the forthcoming sadness that will prevent or buffer how much sadness we'll eventually feel. If we know sadness is coming then we'll be more prepared or at least not as falsely happy so that the switch in emotion will cause a depression. By acquiring this third element of knowledge we have become optimistic by simply acknowledging that the Yin and Yang will occur. Thus, simply allowing the Yin and Yang to occur will be prevented.

If you think that this is simply repeating Yin Yang's philosophy then let's provide an example:
Let's assign numbers to the levels of happiness so that 1= little happiness 3 = very happy and -3= very sad:
If I feel an arbitrary "level 3" happiness then I should naturally assume that I will soon feel a "level -3" sadness to balance it out, by Yin Yang's theory.
However, I'd argue that the realization of Yin Yang's outcomes would make me a) less happy so that I'd end up as a level 2 happy and b) I'd be also more prepared for the eventual sadness so that it would only affect me at a "-2 level of sadness". I also have to take account that not only will I be less sad due to being less happy but on top of that I have further optimism in my dealings with the sadness. So that I'm at a 2:1 ratio of reasons to be happy against sad. Now there are 2 outcomes for this scenario: One outcome is that I'd let the realization of only a level -2 sadness approaching make me a bit happier so that I'm level 2.5 happy expecting a range -2 to -2.5 level sadness.. however, it's not simply not that the the sadder I expect myself, the happier I become since I'm aware of the 2:1 ratio as well (Some may call this hope?). However, as one can tell, this is quite complex and a bit hard to maintain this conscience awareness of ratios which is why one can opt for the second outcome.

The second outcome is (the more pessimistic version) that I don't chose to be as happy and lower my happiness and sadness to the point of level zero. Both happiness and sadness is at a zero level and one stays at a medium. However, knowing one will never get sad by sacrificing happiness is a very peaceful state. Peace is happiness.

Either way, whether one can manipulate the 1:1 ratio of interdependent opposites to a 2:1 ratio or simply nullify the ratio so that it's 0:0 (which is 0) The third element of the synthesis of the opposites occurs by upsetting the balance.