What is the origin of the idiom "when one's back is turned" and when to use it?

The idiom "when one's back is turned" likely has its origin in the idea that when a person's back is turned, they are not able to see what is happening behind them. This lack of awareness can be exploited by others for various purposes, whether it is mischievous acts, pranks, or more serious actions. It is used to describe situations where something occurs or someone takes action when another person is not watching or aware of it.