Taichi might be best translated as Paradox.
Extreme Polarity, Ultimate Limits, or Vital Axis are more literal renderings of the term, but if we want to maximize the efficiency of our understanding, Paradox is the idea we want to discuss.
The fundamental duality of our Reality is expressed as Yin and Yang. Traditional Chinese Medicine says there are two primary forms of Energy (Ch’i), there is Yin Ch’i and there is Yang Ch’i.
Taichi is even apparent at the level of Ch’i.
The arguably most-fundamental substance in the Universe, the Ch’i, is still subject to the principle of Taichi.
Taichi is apparent in all facets of existence.
The uniquely Human polarity of Good and Bad is the most interesting.
All of our desires and preferences have an opposite. I like many things so much, that I can barely tolerate their absence. I am trapped in my preference so strongly that anything other than my preference makes me a mess. Siddhartha Gautama recognized this, which is how he became known as the Buddha.
Much of the difficulty in the Human experience is self-imposed by our strong preferences. We are trapped in the matrix of Taichi, perpetually bouncing between our feelings of highs and lows.
When we have properly understood the nature of Taichi, we can readily understand the value of Wuchi.
Wuchi means that the polarity has been removed, there is no Good or Bad. Wu is emptiness, or non-being. If we lose our preferences, then anything is essentially Good. If we look at things truly and objectively, without filtering information through our matrix of Taichi, the world looks very different than we are used to.
This is the true purpose of all Taichi Practice, to break out of the paradox by seeing the prevalence and absurdity of it. There are numerous beneficial side-effects, which vary by method and intention, but the most important benefit of Taichi Practice is gaining the perspective of Wuchi, which allows you to find Peace despite the constant churning and change that is Life.