This matches my experience. In 2010 I had been using c++ for ~15 years and at that time would have said (correctly) that I knew pretty much the entire language.

This matches my experience. In 2010 I had been using c++ for ~15 years and at that time would have said (correctly) that I knew pretty much the entire language. This was at least partially confirmed by an interview I had at that time for a c++ role, for which I immediately knew the answer to every c++ question. Since then I've continued to use the language daily but have given up hope of ever getting back to that relative level of knowledge. I just try to learn little bits here and there whenever it's relevant to something I'm working on.