One principle is about the fundamental premise of same-difference or connective-separation. The latter pair is more suited to my purpose, as it exemplifies the relation between any 'two.' This could relate not just a philosophical axiom but practically to one person or two people (or more) in my above example. In practicing tai chi alone one is always playing with this ever-changing 'balance' between active and passive between parts of their body-mind, or substantial and insubstantial. And there are several of these balances going on at the same space-time, like between the two hands, the two feet, the head and feet, the front and back, etc. These complimentary parts are connected yet "clearly distinguished."
Where the resistance or pressure comes in is in the dynamic tension between them Note the preposition 'between.' It is what glues them together yet also keeps them apart like a generative (en)closure. I.e, they are adjacent, not one and not two, at least not exactly. This 4 ounces of resistance is strongly akin to any permeable boundary that is both open and closed, that not only separates one from another but also allows connection and communication with another. Hence the practice can also been done with another(s), which experience of working with another feeds back to working with oneself and vice-versa. The training requires both as an ongoing practice. Hence for one is this practice is both/and/neither/nor one/two in oneself and with another.