It is amazing how people ignore facts, and go on what they think is right no matter what.
My favorite foolish statement this time around in this was when someone stated that if electrons went through metal, they would all build up at one end of the cable. Utter lack of understanding how electricity flows through a conductive metal (not a problem), then insisting that this was a fact (problem).
The easist way for your own benefit is simply test for yourself. Cables are always directionally marked, so reverse them. If you don't hear a difference, it doesn't matter to you. The only way that you would fool yourself on this would be if you are using lampchords or some other electrical wire. They aren't marked in what direction that they are extruded, since that detail wouldn't matter for a AC circuit.
Though in reality, cables are directional. It is a basic scientific fact (not theory). The extrusion process creates variation in the way that the metal molicules pack. As the electrons migrate down the wire, the packing variation affects the movement from one end of the wire to the other. This property is called inductance.
From Wikipedia: Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. The magnetic field strength depends on the magnitude of the electric current, and therefore follows any changes in the magnitude of the current. From Faraday's law of induction, any change in magnetic field through a circuit induces an electromotive force (EMF) (voltage) in the conductors, a process known as electromagnetic induction. This induced voltage created by the changing current has the effect of opposing the change in current. This is stated by Lenz's law, and the voltage is called back EMF.
There is more going on than just inductance. But that is the biggest effect and easist to understand.
By training, I was a physical chemist. I did extensive training and study of the packing of molecules.
But unless you insist on being stubornly stupid, don't feel bad. I even had to explain this to electrical engineers, Unless they worked creating audio or video devices, they were unfamilar with the importance of these effects on audio or video equipment.
I remember having a friend over, and he insisted it didn't matter. At the time he did not have very good stereo equipment at home. I reversed the leads on one of my systems, then reversed them back. He looked at me and stated it does matter.
When he bought better equipment and retested directionality himself, he reproduced the effect.
From science, inductance is real, and inductance affects the pathway of electrons through a conductive material. The packing of the molicules will change inductance. Stereo equipment is DC, which is a directional current. Therefore innductance is different in either direction using the same wire. It is a fact on packing variance.