Many of the systems in the world can be classified as chain systems. So knowing what defines a chain system gives you a useful way of approaching them. I picked up the concept from Good Strategy Bad Strategy, Learned from a Master of Strategy.
Pull on a chain, and it breaks at its weakest link. A chain system is one where the weakest link sets the strength of the whole. In other words, when something goes wrong in one part, there is no detour to make up for it.
A supply chain is one example of a chain system. Everything from moving raw materials to the final processing is connected. If any one step is delayed, the whole process is delayed, because no step can be skipped.
In a chain system, the weakest link shakes the performance of the whole. So improving a chain system's performance starts with good diagnosis: you have to work out where the bottleneck is. If your judgment is sound, you can get an outsized improvement with few resources. You might even solve the problem with a surgical strike.
A chain system with no particular bottleneck, on the other hand, is hard to grow as a whole, because every element has to be upgraded a little at a time. That's why a chain system with no weak points is hard to build, just as a hexagonal person, strong in every way, is hard to find. Just as it's hard to find someone who has all of wisdom, virtue, and physical strength. It is hard to become a The Complete Human.
Put the other way around, this can also serve as a moat. It keeps competitors from easily copying the chain. For example, no matter how good a smartphone another company makes, it is hard to catch up with Apple's iPhone. That's because Apple has built a huge UX chain by linking not only the iPhone but also the iPad, Apple Watch, MacBook, and its other devices to one another. To beat this chain, you would have to raise the feel and the integration of every device to Apple's level. It isn't enough for the smartphone alone to be good.
Beyond these business insights, the chain system can also serve as an important mental model for productivity, 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. Much like the supply chain I mentioned earlier. If any of energy, focus, or the right way of taking in and processing information is missing along the way, it's hard to produce anything of value.
Writing, video production, and coding each have their own chain systems. So being highly productive at coding doesn't make you more productive at writing or video production. Still, I suspect there may be a chain they all share. Perhaps writing is the common chain behind a knowledge worker's productivity, because writing is planning ability.