Your knees are on a clock. Poles slow it down.
Downhill is where hiking bills you. Each step is a controlled landing, and your knees absorb several times your body weight — plus whatever's on your back. In your 30s and 40s you absorb it fine. That's the trap: cartilage doesn't send you a warning email.
Planting poles ahead of you moves a real share of that impact into your arms and shoulders before it ever reaches the joint. Do that for twenty years of weekends and it adds up to a completely different set of knees at 60.