I am looking at the classic resistor cube problem-the one in which there is a cube with resistors all of the same value on each side. Particularily I am having trouble understanding the symmetry argument for the case in which the current enters and exits across the diagonal of a face. I realize that two of the sides "by symmetry" are going to be at the same potential. I don't undertand what is meant by "by symmetry." it would be extremely helpful if someone could explain that to me. Thanks.