Hard parts wear and they fail based on how they were manufactured and the two reasons Rich GTP stated. Tie Rods might also wear faster if you're running oversized rims and tires.
The only good thing about outer Tie Rods are that they are cheap and easy to install yourself. You'll have to get a front end alignment done afterward, but all in all the cost shouldn't be much more than about $70 to $80.
Marc
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'00 Trans Am WS6 w/ 25K miles - Lovin' it!!
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RIP '99 GTP w/ 41K miles - Totaled in fire
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RIP '97 GTP w/ 192K miles - Totaled when broadsided