To return to the beginning or starting point, especially after a failed attempt or when previous progress has been lost.
This phrase likely comes from early British radio broadcasts of football (soccer) matches in the 1920s-30s, where the field was divided into numbered squares on printed diagrams. Square one was near the goal, so 'back to square one' meant the ball had returned to the starting area after an unsuccessful play.
The phrase captures the uniquely modern frustration of having to restart complex processes - something our ancestors rarely experienced on such a scale. Interestingly, while we associate it with failure, in the original football context, being back to square one just meant the game was continuing normally, not that anyone had failed.
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