You’ve just shifted the goalpost twice here. I never learned about Paxos, but I did learn about consensus algorithms. Second, learning about something, and implementing something are completely different. Most CS graduates have an idea of how syntax parsing works. How many can implement a parser? What about a syntax highlighter? Most graduates have an idea of how an OS works. How many can build an OS?

I guess if you’re always using libraries though, you may mistakenly be thinking that these libraries are just doing trivial work. Once you dive in and try to implement the low level stuff, then you realize how big of a disconnect there is between a fuzzy idea in your head and the lines of code that constitute that idea in reality.