Many systems are chain systems. So knowing the characteristics of a chain system can give you real insight.
Pull on a chain and it breaks at its weakest link. A chain system, in this sense, is a system where the weakest link determines the strength of the whole. In other words, it's a system with no detour when something goes wrong in any one part. Supply networks, for instance, are often called supply chains. Everything is connected — moving raw materials, processing them, and finally turning them into a finished product. If any one of those steps falls behind, the entire process falls behind.
Because the weakest link shakes the performance of the whole, improving a chain system's performance depends on getting the diagnosis right. You have to correctly identify where the bottleneck is. If your judgment is sound, you can get a remarkable improvement in results while putting in very few resources.
A chain system with no particular bottleneck is hard to improve overall. That's because you have to upgrade every element a little at a time.
But flip that around and it also functions as a moat. It keeps competitors from easily replicating that chain. No matter how well another company makes smartphones, for example, it will struggle to catch up with Apple's iPhone. That's because Apple built an enormous UX chain — not just the iPhone, but its integration with the iPad, the MacBook, and the rest. To beat that chain, you'd have to raise the feel and the integration of every device to Apple's level. It isn't just the smartphone that matters.
Beyond business insights like these, the chain system can also serve as an important mental model for productivity. That's because productivity itself is a chain system. To produce value in knowledge work, you need enough energy, you need to focus it where it's needed, and you need to process information appropriately. If you lack energy, focus, or a way to take in and process the right information along the way, valuable output becomes difficult.
Writing, video, coding — each of these has its own chain system as well. So being highly productive at coding doesn't mean you'll be highly productive at writing or video production. Still, I have a feeling there's some productivity that's common to all of them. Writing, perhaps, is the shared chain system underlying a knowledge worker's productivity. Writing is planning, after all.