I've had cables go bad in multiple sets of headphones that I barely even used, let alone subjected to the expected rigors of travel or heavy use. As far as I can tell, a lot of cheap 3.5mm plugs have strain relief that's basically just ornamental, and even a modest amount of flexing or vibration will quickly break one of the wires.

>What were you doing with your headphone cables?

Getting them caught on door handles, mostly.