DEFINITION of Weak Sister

"Weak sister" refers to an element that undermines the entire system. It can either refer to a single individual or a specialized group considered to be the weak link in an integrated process.


Usually referring to an undependable, poorly performing member of a group environment, the weak sister can also be a malfunctioning part of a team-oriented task. For example, the slowest member of an assembly line or a slow marketing team that hinders the overall performance of operations is referred to as the weak sister.

'Weakest Link in the Chain'

The term “weak sister” is similar to the term “weakest link in the chain.” If you describe someone or something as a weak link or a weak link in the chain, you mean that they are an unreliable part of a system or member of a group, and because of them the whole system or group may fail.

People also say that someone or something is the weakest link if they are the most unreliable part of a system. There is an adage that a system is only as strong as its weakest link. A rail system is only as strong as its weakest link, as any commuter trapped behind a broken-down train can testify.

The term “weakest link” came from the proverb “A chain is only as strong as its weakest link.” In other words, one substandard link may cause a chain to break, even though the other, stronger links may hold when put under pressure. This proverb may be traced to the work Essays on the Intellectual Powers of Man, authored by Thomas Reid in 1786: “In every chain of reasoning, the evidence of the last conclusion can be no greater than that of the weakest link of the chain, whatever may be the strength of the rest.” It is safe to assume that the proverb was in general use long before it was published.

Examples of Weak Sister/Weakest Link in the Chain

“A fresh batch of China’s smaller regional lenders are poised for initial public offerings (IPOs) on the A-share stock market this year, but their aggressive style in expanding capital levels is making them arguably the weakest link in the country’s financial system, according to analysts.” (South China Morning Post)

“Prime Minister Malcolm Turnbull has acknowledged foreign agents may be trying to gather compromising material on individual Australian politicians through cyber attacks, while a Labor MP has said parliamentarians themselves are the 'weakest link.'” (Sydney Morning Herald)