Agreed. I don't know anything about turning sand into transistors or assembly but do well. So I don't know my full stack either.

What is important is not being afraid to learn the rest of your system and keeping an index.

Most importantly it's about being able to spin up on anything quickly. That's how you have wide reach. Digging in when you have to, gliding high when you have to. Appropriate level for the problem at hand.

When I was in college eons ago they taught CS folks all of engineering. "When do I need to know chem-e or analog control systems?" We asked. "You won't. You just need to be able to spin up on it enough to code it and then forget it. We're providing you a strong base."

That holds even within just large code bases.