When you think about the aggro that chains have to take it amazes me that chains of any description don't break more often.
After all, all the power of the bike gets transmitted through the chain, along with a bit of whiplash as you get in and out of the throttle, and every bit of the chain has to take the same amount of tension.
When you think that every one of those little pins has to take the same load...
When you think of the huge number of chains produced as well, statistically, every manufacturer is bound to produce a duff one that creeps through quality control every now and again