There is a historic site, a restored gristmill, near where I grew up. It is a good historical site, and they often took us there on school tours.
When I was little, the place seemed massive, complicated, and very impressive. It was an unfathomable maze of gears, machines, and tubes for transferring and processing the grain. I understood how the simple stone-grinding for cornmeal worked, by the power from the waterwheel, but the section with the roller mills for wheat remained an unknowable mystery.
I went back last weekend. I immediately noticed that the place seemed small. That was to be expected; I have grown up and seen a lot of things since I was last there. But what really struck me, when I got inside, was how simple the place was. Within a few minutes of looking at the machines, I could understand exactly how everything worked. The arrangement of roller mills and sifters was simple, obvious, and easy to understand. I could visualize the entire process.
This experience was a big lesson how much the human brain develops as it matures. Kids can only understand what is right in front of them. No matter how clever they are, they have trouble understanding long-term consequences, big webs of causality, or large interconnected systems. The ability to understand the 'big picture' and act according to that knowledge is a big part of being an adult.