Comment by jahnu
30 year c++ veteran here. Also don’t know 80%. I used to know more but a combination of way better tooling and “modern” c++ and most importantly realising that thinking more about things other than the language details led to better software meant I have forgotten stuff I used to know.
Sounds like the 80/20 rule but applied to mastering C++ features. Which honestly makes sense to me, and doesn't even feel C++ specific, really. It just becomes more applicable the bigger and more complicated a language gets.