What is the origin of the idiom "the final nail in the coffin" and when to use it?

The idiom "the final nail in the coffin" has its origins in the act of nailing shut a coffin after a person has died. It refers to the last event or action that seals the outcome and makes it irreversible. The phrase can also be used to describe the point of no return, where there is no possibility of recovery or redemption.