Could build a lathe from parts they could purchase, but not from scratch. The simple ballpoint pen is an absolute marvel of precision engineering that we take utterly for granted. That ball in the tip? Not something you could knock out in a weekend by hand. Even wire itself as a basic component is freaking impossible to feasibly do from scratch compared to going down to the hardware store and spending $5 for a spool. That I can also get a microcontroller devkit that's impossible for me to recreate from a local store is mind-blowing, if we stop to think about it.

2000 years ago the person who was capable enough to think of and build a lathe didn’t go to order the pieces. They modeled the raw materials (wood, metal, stone) into what they needed. But let me give you a less debatable example. Watch makers or even the people who built the Antikythera mechanism didn’t go to the cog and sprocket store to get the parts. They manufactured the components from the raw material or as close to it as possible. They probably built their own tools to for the longest time.

And when I said pen I meant fountain pen. It’s counterintuitive but probably more people today can draw a conceptual diagram of a ballpoint than a fountain pen. Ballpoints are a very simple design limited only by the very tight tolerances need to make them work.

But that was my whole point, complexity got so high that most things around us cannot be built without specialized tools, specialized building blocks, and specialized knowledge that takes years to gather. And this needs to be repeated for almost every object. Different tools, building blocks, and knowledge.

A highschooler today knows more chemistry than Mendeleev but that doesn’t help because the complexity in each field or product increases faster than one person’s ability to keep up with learning.