Perhaps, 'laws' would have been a better word than 'rules'.

I was thinking of it more in terms of complexity. When things are looked at in isolation, it is much easier to see how the simple laws apply. But as things get more complex, we also need to figure out how the different systems interact and influence each other. This makes the simple laws harder to discern.

Simple  systems  have few components and their behavior is in all respects fully  understandable and  predictable. An example would be a solid ball  falling under the action of  gravity through air. This simple system consists of the ball, the air, and the gravitational force.  Here we usually assume a single ball, constant acceleration of gravity, a viscous drag on the ball,  and Newton’s laws. When making these assumptions, we arrive at very useful answers. We did,  however, neglect many aspects. If, for example, we would ask how the behavior changes when  we go from one ball, to two, to three, or even more balls that fall close to each other, our “Simple  System” assumption fails. It is not sufficient to generalize from one ball’s  behavior to many.  Instead we need to consider the interaction of the balls through their self‐generated vortices.