Mine failed because something lodged in one of the jockey wheels on the rear derailleur, I was going uphill loaded, and I forced the pedals when it locked up. If I had stopped, and checked for the problem, I would not have broken the chain. But I did not, and broke the chain. I repaired roadside with no difficulty. Now I carry a spare chain, not much weight penalty in the total perspective: rider 195, bike 30+, gear 40+, spare chain a few ounces.