Originally Posted by FBinNY

........Whether your chain breaks sooner or later, or never depends mostly on how you shift combined with luck, since it only matters if the shift force is applied to that one joint. So it's about a one in a hundred chance for each bad shift, but keep it up and your luck will run out.

BTW- most people never break chains, but it can happen to anybody. However if you break more than one chain in a lifetime it's probably not just bad luck.