[ajdegol]

Simple systems can indeed be made of complex components; however it is a measure of interconnectedness. The key concept is that we can only hold a finite amount of complexity in our heads at any one time, and so if we can minimise that we can be more efficient and effective.

The analogy is a lego castle vs a wool castle. A lego brick is very simple and contained, and from this you can build wonderful structures; in addition if you wish to change out a portion it is easy to do because changing on part of the system (i.e. implementation) doesn't affect the rest so long as the contract between components is maintained.

Contrasting: should you pull on a thread in a wool castle it will affect other parts of the castle. A lot of software is like this, which makes it very hard to reason about.

[hyperpallium]

"Interconnectedness" is also a measure of resistence to hierarchical decomposition (or factoring ax+bx -> (a+b)x); irreducable complexity.

One technique is redefining the problem, to smaller or bigger:

Work on only part of a problem, a subset, leaving something out. e.g. git's data model does not represent renames as first class constucts, enabling it to be disproportionately simpler.

Expand the problem, a superset, to integrate lower or higher level or associated parts that aren't usually included. Previously scattered commonalities may then appear, enabling decomposition.

[roenxi]

And the Lego analogy works in particularly nicely considering just how much effort, precision and design work needs to go in to making the blocks simple [0]. This is a nice analogy for how keeping software components simple and making them interface cleanly is a difficult task.

[0] https://en.wikipedia.org/wiki/Lego#Design