say you're cruisin along at a good clip, and say you go into a skid.. the hub/cog/lock ring will be stationary, but they sure as hell want to be spinning. as you know, the lock ring is there to keep the cog from spinning itself off, which is exactly what it wants to do in this situation. the cog, trying to spin itself off the hub, will press on the lock ring quite hard. sometimes, hard enough to damage the threads holding the lock ring on.