The December 21, 2019 edition of The Economist had an article about the Taiwan Semiconductor Manufacturing Company's plant known as Fab 18. In just a few paragraphs the article explains something that I have been wondering about: We hear that some of the modern chips have millions, or even billions of transistors on them. Who could possibly design at that level of complexity? The article provides the answer: humans don't do it. These chips are really designed by other computers (see above).
I don't like to use integrated circuits because they often seem like mysterious black boxes I want to be able to understand how the rig I build really works. Some ICs do allow for this kind of understanding -- you can get the internal wiring diagrams for an NE602, or an LM386, for example. You can study them and gain an understanding. Those little black boxes then become less mysterious. But that kind of understanding is just impossible with the kind of modern microprocessors churned out by Fab 18. No one really knows how these chips work:
"The circuitry is not as complex as, say, the human mind, but it is far more complex than any human mind could fathom."
Sorry, but I prefer fathoming. Please pass me some 2N3904s.