Weakest Link
The term given to a component in a system that is most likely to fail, regardless of the strength of adjacent components.
Origin
Scottish philosopher Thomas Reid used the chain metaphor in his 1785 Essays on the Intellectual Powers of Man, writing that "the evidence of the last conclusion can be no greater than that of the weakest link of the chain." Reid applied it to chains of reasoning, but the metaphor generalized naturally to any system. The full proverb "a chain is no stronger than its weakest link" first appeared in print in Cornhill Magazine in 1868, and similar sayings — like the Basque proverb "a thread breaks where it is thinnest" — suggest the idea is ancient and cross-cultural.
Everyday Use
Your home security is only as good as your flimsiest lock, and your project team is only as reliable as its least dependable member. We invoke the weakest link whenever we recognize that one vulnerable component can bring down an otherwise strong system — whether it's a flimsy password in a security chain or the one unreliable supplier in your logistics network.