Chain-Link Systems

If a chain must not fail, there is not point in strengthening only some of the links.

A system has a chain-link logic when its performance is limited by its weakest sub unit, or "link."  Where there is a weak link, a chain is not made stronger by strengthening the other links. 

For the space shuttle Challenger, the weakest link was a solid rubber O-ring.   On January 28, 1986, the O-ring in Challenger's booster engine failed.  Hot gas knifed through the structure; the rocket exploded.  Challenger and its crew, the "pride of our nation" President Reagan called them, tumbled out of the clear blue sky and shattered on the ocean sixty-five thousand feet below.

If a chain must not fail, there is not point in strengthening only some of the links.  Similarly, for Challenger, there could be no gain to making the booster engines stronger if the O-ring was weak.  There was little point in improving guidance, or communications, or increasing the quality of crew training, if the O-ring was weak.  

ACTION POINT: The logic of the chain is at work in situations ranging from mountain climbing to the space shuttle to aesthetic judgement--situations in which the quality of components or sub parts matters.