I think it's after developing and running a few real world large systems over the course of years. I was an extremely technical "junior" engineer, and I often k

I think it's after developing and running a few real world large systems over the course of years. I was an extremely technical "junior" engineer, and I often knew things that "senior" engineers didn't, but there really is no substitute for real world experience over time. It's a bit like how life works in general. You "level up" every 7-10 years and look back at how "dumb" you were previously. After a few cycles of this you get to a point where you're an "adult" in most of the ways that matter. A relevant quote from @KentBeck really nails the value of experience: "first you learn the value of abstraction, then you learn the cost of abstraction, then you're ready to engineer"