"[stab] {sb} in the back" の定義と意味

What is the origin of the idiom "stab someone in the back" and when to use it?

The idiom "stab someone in the back" has origins that date back centuries and are rooted in the idea of treachery and betrayal. The expression draws a vivid image of someone being betrayed by a close friend or ally who literally stabs them from behind, catching them off guard. It is used to describe an act of betrayal or treachery by someone who was previously considered a friend, ally, or trusted individual. It suggests that the betrayal was done secretly or behind the person's back, without their knowledge or awareness.