I have been programming in C++ for decades and I am humbled every time I read Scott Meyers "Effective Modern C++". I still can't figure out when an r-value is d

I have been programming in C++ for decades and I am humbled every time I read Scott Meyers "Effective Modern C++". I still can't figure out when an r-value is different than a universal reference. I don't think really anybody is a C++ guru anymore. If someone says they know Modern C++ I am almost sure they don't.