answer:The answer, I think, is that cheap headsets will (eventually) die on both sides, but you only hear it die on one side, because at that point you set it aside and replace it. Of course, there’s always the headphone jack itself to consider. If the plug isn’t inserted to its “home” position, then one of the sides is going to be cut off. I’ll try to find a link that describes the jack / plug positioning. You may be able to test this yourself, though, if you have a functioning set of headphones (both sides working). Pull the plug out of the jack by even as little as 1/16” inch or so, and one of the sides will cut off. Edit: Here is a view of a headphone plug (mini stereo plug, as found in most computers now). You can see from the diagram how little margin there is for error on the “left channel” plug here. If it doesn’t seat right in the jack, because of any interference from foreign material in the jack or damage to the plug (or the jack), then you simply won’t get any current to the left channel, and therefore no sound.