Did you ever try to work through Jack Crenshaw's "Let's build a compiler"? Remember the early point where you add a line of code and "CONGRATULATIONS! You have just written a working compiler!"?
Well, I just ported that one line (and the page of helpers backing it) to my own assembly lang, and it only took me 2 months to do it 😂
In my defense:
a) It's *thoroughly* unit-tested asm, and
b) I had to rethink the design of a couple of OS syscalls to make them testable.