> Can humans understand the IP protocol? The TCP protocol?

Yes, but you have to frame the exchange correctly or people will look at you strangely when you start addressing and acknowledging them.

I mean, not over the wire, but an average developer can definitely grok either protocol pretty quickly. IP is connectionless and fairly simple. TCP requires a more complicated state machine, and has more extensions if you want to implement the entire thing. IPv6 makes both more complicated. But the actual functionality is limited, so there's not a lot of complexity outside of "Did they turn on option 1? Do a thing. Did they turn on option 2? Do another thing. Is option 2 on but option 3 off? Do another thing."

It's not like implementing transport encryption and multiplexing and congestion control and etc etc etc. I doubt many people in the world actually know how to implement QUIC. I implemented tcp/ip as a teenager when I was bored over summer break.

Oh sure, they're not even that complicated. I've been asked (and asked myself) about them in interviews.

They are pretty easy compared to the others mentioned