The Tenth Man strategy says that if nine people agree on a particular course of action, the tenth person must, in the context of the strategy, take a contrary approach so that all alternatives can be considered.
What are the origins of this rule? How far back does it go? Are there any primary sources (or quotes from prominent persons) related to the rule?
I've never heard of this rule, but there is somewhat of precedent in term "Devil's Advocate" which is someone who takes an opposing position for the sake of argument.
Originally this was the name of a church official chosen to argue the contrary point of a vote on canonization.
I believe it was a fabrication for World War Z, 2006, a great novel.