https://en.wikipedia.org/wiki/Samuel_Slater
> He memorized the designs of textile factory machinery as an apprentice to a pioneer in the British industry before migrating to the United States at the age of 21. He designed the first textile mills in the US and later went into business for himself, developing a family business with his sons.
Slater memorized these trade secrets, because any papers containing these designs would have been confiscated from him.
Consider also the brain drain, wherein educated professionals have, over the past few decades, been siphoned out of the developing world, attracted by higher remuneration in the West. This is not a dissimilar process, but it is operating in reverse.