I have had six iPhones and more chargers than I care to count and have found that the chargers all fail in the same way. At some point, the wire right by the Lightning connector starts to fray, eventually splitting the rubber tubing and finally barfing some blue-green type of rust all over the rest of the cord. I have literally had 10 cords do this to me, always in the same spot and I ask Apple to come up with a solution.
I am fairly certain why it happens, people constantly twist the cord to get it to stick into the connector although you would have thought that with the double sided lightning connector this would be minimized
But now I am stuck with yet another failed cord which does me about as much good as a broken shoelace and there I go again buying another piece of electronic crap and increasing my carbon Apple footprint