Originally Posted by
Velo Dog
Not that you'd want to follow my example for maintenance, but I've been riding for more than 40 years, owned at least 15 bikes (plus maintaining my wife's and kids' rides), and I've only seen one cable fray. I replace them occasionally, usually when I replace the brake pads, which I do when they look like they need it. But as far as I can tell, cables last forever.
Get back to us when you've worked for a high volume road shop, for a while.
Home wrenching is completely different than shop wrenching. And your experience, unfortunately does not reflect reality. Cables will fray usually at the anchor point where they've been crushed. Rear Derailleur cables especially will tend to break off at the head, leaving the rest stuck in the shifter. This is not good for shimano STI's.
Brake cables are much more durable. You don't need to replace these periodically, only when there seems to be a problem. You'll likely get contamination/rust that requires replacement before you break one.