The really short summary is that C++ provides abstractions, which allow to write more complex code simpler while many of those can be eliminated by the compiler

The really short summary is that C++ provides abstractions, which allow to write more complex code simpler while many of those can be eliminated by the compiler leaving no runtime overhead. Sure there are things (i.e. virtual classes) which cause an runtime overhead, but even when doing the same thing in C you'd need similar logic to what the C++ compiler produces for you.