What is the origin of the idiom "sing a different tune" and when to use it?

The idiom "sing a different tune" likely originated from the world of music, where a change in tune or song signifies a shift in mood, perspective, or behavior. It emerged as a metaphorical expression to indicate a change in one's attitude, opinion, or approach to a situation. The phrase is used to convey the idea that someone is altering their stance or behavior, much like a musician changing the melody or lyrics of a song.