Originally Posted by JonOnWheels

...And that's what's so strange here. The mechanic was certain that I was riding only on the smallest cogs because those are the only ones that appeared worn to him. I know I don't do that. While it makes no sense that any cogs would wear out so quickly, it makes particularly no sense that it would be the smallest cogs. That's why I posted the question, to see if anyone has a theory how this could have happened. The bottom line is that it did happen, and I'm trying to get a handle on why.