On the nail

(UK) immediately, without delay

"Tell me, have you a mind to anything in the Doctor's book? Speak the word, and I will help you to it upon the nail." --Thomas Nashe, Have With You To Saffron Walden (1596)

Etymology: On the nail allegedly from the tradition of striking bargains by placing cash on the nails in Bristol. The Oxford English Dictionary however cites a Anglo-Norman phrase from c. 1360, "payer sur le ungle" to pay on the (finger)nail, meaning "to pay immediately and in full", and quotes parallel usages from 17th century French, Dutch and German sources. It adds that "N.E.D. (1906) notes that: ‘the explanations associating it with certain pillars at the Exchange of Limerick or Bristol are too late to be of any authority in deciding the question’."

source: wiktionary

A chain is only strong as its weakest link

Meaning: An organization (especially a process or a business) is only as strong or powerful as its weakest person. A group of associates is only as strong as its laziest member.

Origin of the proverb: This originated in the United Kingdom (UK), hosted there by Anne Robinson, and was later syndicated for use in many other countries. The show, which relies on the demonstration of the abysmal lack of general knowledge by many of the participating contestants, is an example of the many 'humiliation television' shows of the early 21st century and is a sad spectacle. It is clearly a literal fact that a chain is only as strong as its weakest link. The conversion of that notion into a figurative phrase was established in the language by the 18th century. Thomas Reid's Essays on the Intellectual Powers of Man, 1786, included this line:

"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."

source: www.phrases.org.uk, wikipedia