Two causes for failure other than it just wearing out. It has a ceramic tip within the "nose" so don't drop it at all costs. Treat it literally like glass as dropping it on your garage floor will probably destroy it. Also, the new sensor will come with a gray anti seize paste on the threads. Take care not to transfer any of that paste to the "nose" of the new sensor on your fingers when handling it. It will shorten the life of it considerably. SOme guys also seem to think that running off brand, rot gut gas (the stuff some convenence stores sell that came from who knows where) is bad news for fuel injection systems overall as it doesn't contain any cleaning additives so deposits build up on injectors etc. including the O2 sensors.

Are you sure it's bad as in did you get a CE light/fault code? There are instructions for cleaning an O2 sensor on the board that uses brake cleaner and a propane torch that may be worth a try before investing in a new one. I haven't been able to locate it but hopefully one of these guys will know. Also, avoid "aftermarket" sensors. Get Bosch and double check to make sure it is the correct one for your engine.

bl