What’s this? Learn C++ before C#... Why though?!

Question

I’ve seen this said all over the place, but no one goes into detail explaining why. What are the advantages vs. disadvantages for learning C++ before C#? Up until now I’ve became curious about how programming really works. What happens underneath it all? What happens when I compile it and run my program? Is this what they mean by learn C++ first? Will it help me to understand what’s going on more clearly? BTW, I already know C#. Thanks, John