I can reason through the code and understand it.
The thing that makes me wonder if I'll ever be a real programmer when I grow up is that someone wrote this, probably on a Thursday after lunch (at least, that's how my brain imagines it).
They were able to conceptualize the math solution to a major optimization problem, deal with all sorts of precision issues with bit manipulation, and come up with a blazing fast bedrock algorithm that's dazzling both in it's simplicity and complexity. And then likely popped out to a pub for a pint and didn't think much about it again.
Intellectually, I understand that this person was specialized, and may struggle mightily navigating the complexity of modern web frameworks, something that I find straightforward because I do it every day.
But for some reason, this stuff always strikes me as being "real" programming, and what I'm doing as just plumbing, piping together the bits that the "real" programmers write.