That said, the fault is not his. Shitty udacity never ever mentions they are for beginners. They sell it as "career changing". So blame is on them.
A large portion of learning material (feels like >95%) caters to beginner or junior level people. Very rarely do you find books or tutorials or material meant for those beyond the junior level.
Even the "advanced" or "intermediate" videos on places like Pluralsight, Lynda, etc feel like it's barely a step above beginner. I don't have much experience with Udacity but I'm guessing it's the same?
It seems, IME, like the only way to learn the intimate/advanced knowledge is to talk to core developers or others who have a similar problem domain.
It feels like for every C# in Depth or YDKJS there's 100s of other resources strictly for the beginner. It's just hard to sift through 100s or 1000s of resources before you find something worthwhile.
after that, you have better honed long tail search queries for online.
One simply has to muster up the motivation and effort to seek them out.
Honestly the best way to improve, IMO, is to just start participating and contributing.
"I hear and I forget. I see and I remember. I do and I understand."
-- Confucius