A well considered article by David R. Blossom, ALCM, CFPS, CFII posted at www.FireEngineering.com answers this question. Click on the link to the website, then Search for the Keywords “weakest link.” (Free registration required to read the article.)
Quote: “The old adage that a chain is only as strong as its weakest link is a perfect description of fire protection systems. However, can you think of a more potentially weaker and extremely important link than a hydrant that doesn’t work?