Why do cables need break-in?

When cables are cast the materials form a crystaline structure (which those of us in the audio world refer to as "grain" ).This stucture is relativly random . However,after several hours of use the cable developes a more consistant patern.Thus, creating an easier line of travel for the electrons to follow.

This is not permanent. If you did not use the cable for an extended period, you would have to break them in again.

Why do amps, pre-amps, cd players, speakers, cartridges, and everything else in your system need to be broken-in? The reasons are complex, but the simple answer is that the wire has a crystaline structure that presents many options to the electrons as they negotiate the path one copper molecule to the next. For the first few hours of use the electrons will be seeking the path of least resistance between every molecule. Once that path is discovered, the current flow is much smoother even though the resistance doesn't change. If you take your cables and disconnect them, roll them up and store them, the path will be lost and you'll have to break them in again. Yes, the same holds true for interconnects.