What is the origin of the idiom "nourish a viper in one's bosom" and when to use it?

The idiom "nourish a viper in one's bosom" can be traced back to ancient Roman mythology and Aesop's fables. The phrase refers to the story of a person who unknowingly takes care of a venomous snake, symbolizing a treacherous or deceitful individual. It is used to caution against misplaced trust or being too generous to someone who does not deserve it. It is often employed to describe situations where someone is deceived by a person they had trusted or helped.