There is an article on Mokuren Dojo that observes that whenever uke is moving, uke is off balance.

Hmmm … wow. That observation seems pretty much the key. Unless uke happens to be the one-in-a-million t’ai chi master, working with that tiny amount of energy (as opposed to the proverbial 1000 lbs of force) is all one should need to disrupt uke’s balance and thereby gain control in the most efficient fashion. Getting to that internal arts goal of on first touch the opponent’s balance has been taken and the opponent is sent flying. Even well balanced people are off balance quite a bit. Something tells me this lesson all comes back to zhan zhuang somehow. The would be “master” needs to have supreme understanding of balance. This statement must not apply to this would be master. In a reductionist theory approach, that’s all there really is. This statement holds the entire key, at least for stand-up off-balancing/throwing approaches. Everything else is an “application” of, or an elaboration on, this sort of mathematically reduced-to-its-essence formula.