What is the origin of the idiom "square one" and when to use it?

The idiom "square one" is believed to have originated in the game of Snakes and Ladders, where players who land on a snake's head are sent back to the beginning of the game. In modern usage, it can refer to any situation where a person or group has to start over from the beginning. It can apply to personal or professional contexts, and can refer to both minor and major setbacks.