What is the origin of the idiom "play by ear" and when to use it?

The idiom "play by ear" has its origins in music. It means to perform a piece of music without relying on sheet music or formal notation. Instead, the musician plays based on what they hear and feel, often improvising as they go along. The idiom likely emerged from the world of jazz and other improvisational music genres. This expression is not limited to music and can be used more broadly to describe the act of handling a situation or making decisions as they come, without a predetermined plan or set of instructions. It implies adaptability and the ability to respond to changing circumstances.