I don't think there is one answer but there are a few things I have noticed in my short career so far:
* I think an intermediate level of mastery is when you realize that a computer is a logic machine built to serve humans and it will always listen to you if you're willing to put in the effort. You can always go a level deeper. Great engineers know all of the tools at their disposal and will bend the computer to their will if they need to. At the same time, they know the difference between a great low-level solution and a shoddy hack.
* Our industry is one of the few where we spend the majority of our time fixing our own mistakes. We call these mistakes "bugs" but they don't just appear, we produce them. The best engineers produce fewer bugs than they fix and rarely end up in a "whack a mole" situation where fixing one thing breaks another thing.
