What is the origin of the idiom "draw the line" and when to use it?

The idiom "draw the line" originated from the act of physically drawing a line to demarcate a boundary or limit, symbolizing a clear separation between two sides. Over time, the phrase evolved into a metaphorical expression, often used to signify setting a limit, establishing a point beyond which one is unwilling to go, or indicating a boundary that should not be crossed. It is commonly employed to convey a firm decision or establish a clear distinction.