I am confused as to why storing a reference to a member variable with an alias allows us to access it, while storing it with a variable does not allow us to access the same variable.

Let me clear up what I mean, say we have class Journey:

class Journey {
  protected:
      Coordinate start; //coordinate consists of x and y values
  public:
      Journey(Coordinate startIn,): start(startIn){} 
  //methods ......
  Coordinate & getStart(){ //returns a reference to the "start" member
    return start; 
  }
};

• now say I do this

int main() {
    Journey j(Coordinate(1,1));
    Coordinate & a = j.getStart();  //function returns a reference and is stored under the alias "a"
    a.setX(0); //changes X value of the "start" member variable
    cout << j.getStart().getX() << endl; //returns 0 - as expected!
}

• the example above works as I returned a reference to the member variable “start” and stored it under an alias and I accessed it to change the original member variable

• But say I stored the reference to start under a variable instead

int main() {
    Journey j(Coordinate(1,1));
    Coordinate a = j.getStart();  //function returns a reference and is stored under the VARIABLE "a"
    a.setX(0); 
    cout << j.getStart().getX() << endl; //returns 1 - Original start was not changed?
}

• I cannot do the same as a does not access the start member variable

I am not sure why this happens? What happened behind the scenes? We are storing the reference to start under a variable instead of an alias.