A quality earpiece mostly differs from a low quality one by the quality of the cables (as well as the plastic parts). Good quality cable lasts much longer. Probably 9 out 10 earpiece failures can be attributed to cable faults. These faults are caused by the copper conductors being damaged and then broken. These faults are nearly always invisible.
Soft and Flexible
Good quality cables tend to be soft, flexible and resistant to snagging. Soft and flexible means they hang or drape better, closer to the body and less prone to snagging.
If cables do become snagged the outer insulation can stretch but the copper conductors do not so either they tear or they are torn from the parts to which they are soldered. To prevent this happening good quality earpiece have what is often termed a Kevlar braid.
Kevlar is a brand name of one of several Aramid fibres. They have the properties of being strong but very low stretch. If these are laid alongside the conductors in a cable they help prevent the cable stretching and becoming damaged. Many good quality earpieces have a fibre of the sort in the cables.
The other failure of the conductors is caused by repeated sharp bending where the cable enters a plug, Mic or earpiece. Well designed earpieces have an extra outer sheath or strain relieve in these areas to prevent the cable being kinked or bending sharply.