Someone used a basic #2 pencil as an example. Traced all the people involved to produce it. Back from the manufacturing, through the guys who drive the trucks full of raw materials, through the guys who mine the raw materials, through the guys who manufacture the equipment required for the mining, through the company that makes the gas for the mining equipment, the people who make the equipment for the oil refinery ... etc ... etc ... etc ...
If all the technology went away tomorrow, and we had to start over really from scratch, even if we still had the knowledge we couldn't do it in two lifetimes.