So, a Living Being is composed of multiple parts who act pretty much on tandem except extreme situations like Cancer, how does that work?
The Republic is about this. As is Moby Dick though it is not explicit in the latter whereas the metaphor is explicitly declared in the former. Plato's stuff actually makes even more sense if you append the death of socrates cycle to the end of the republic. First you instantiate the philosopher king who puts the house in order, then the philosopher king commits suicide as a logical result of the rules as set up by that very same philosopher king.
how does that work?
Well, generally, it works by cycles of fascism and revolution - the strongest part controls things, until it doesn't, and things break down for a while. After some intervention (nap/medication/surgery/etc.), control is re-established (or the being stops living). To the extent that the control is less severe, it lasts longer but diverges a bit more from it's preferred directions.
This applies both to subpersonal (akrasia and willpower) and interpersonal (political power) cases. It kind of fits cancer/illness as well.
It is open to debate whether other, more pleasant models are possible to implement.