Why can you indirectly bind an rvalue to an lvalue reference but not directly?

Question

From what I\'ve read and seen you cannot bind an expression that is an rvalue to an lvalue reference. What I have seen however is that you can bind an rvalue to an rvalue refere

Answer 1

When you call foo(1), a temporary int equal to 1 is created, and int&& a is bound to it. You can freely change it. The same way you can write int&& a = 1;. a itself is an lvalue, so you can bind lvalue reference to it.

You may read a great article Universal References by Scott Meyers which explains rvalue and lvalue references in detail.