One big clue about the nature of break-in. Memory.
We know that once broken in, cables and components retain many of the benefits earned through extended playing time.
If we put our Sherlock hats on we could make some guesses as to what kinds of characteristics are capable of being stored.
Capacitors change character after voltage has been applied to them in a process called forming. Forming changes the oxide layer of the insulating dielectric necessary for the capacitor to function properly. Over time and use, this layer's thickness can change for the better. And there are other changes to capacitors as well.
Cable insulation can also retain a charge. AudioQuest (among others) actually add a battery to throw a high voltage on the insulation for better performance. Something similar happens when we run electrical currents through the cable.
Whatever is happening in break-in, the effects last for some time before the device or cable slowly reverts back to its original state.
If we don't know specific answers to unanswered observations, we use clues to help us reverse engineer the answer.
