A baby doesn't grow like how a toy doll is put together, from a few large parts. A human body starts with just a few cells. Each cell is like a chemical factory that produces new cells and everything. New cells are build molecule by molecule. Molecules are of nano scale. Every living organism is build up in nano-style.
If we want to build super stuff, we should learn how to build on a nano scale, even really big stuff like buildings and bridges. Most stuff we make is very chaotic at nano scale. Animals and plants and even crystals are all beautifully organized at nano scale.
We people are like dinosaurs. We are so big relative to a bacteria, we're made of billions of cells. To a bacteria, the old dinosaurs were just slightly bigger then us humans.
The process of building big things the nano-style must be an automatic happening, a chain reaction, because it's quite impossible to build something big molecule by molecule and be ready before the end of time. So; it can't be done serial, the immense amount of works need to be done parallel.
To get a certain result, a large object build nano-style, the designer has to program a certain chain reaction.