A piece of technology that requires me to learn so much about it that I understand intimately what's going on under the hood such that I could re-implement it m

A piece of technology that requires me to learn so much about it that I understand intimately what's going on under the hood such that I could re-implement it myself? That sounds lovely, but honestly when that happens I regard it as a failure. That means its abstraction is so porous that I'm constantly having to think about what it's actually doing. I think about the frameworks and libs where I know every iota of them... and it's not the good ones. It's the crappy ones where I'm constantly having to debug the sharp edges. "Why the heck does it do this? Ohhhhh, that's why."