I agree it's incredibly important to dig into layers under (and over) the one you're working at! I'm very grateful for the experience of building a simple unix-like kernel and a simplified TCP & IP implementation as school projects. And I'd encourage anyone to do the same with HTTP 1 or 2 or 3. The difference is that no one thinks that their educational/toy TCP implementation is suitable for production use, while people do seem to (mistakenly) think that about HTTP.