Pull the pin on something

To pull the pin on something is to abort or end a relationship or project etc, and this figurative use dates from the late 1920s. The pin is not thought to be the pin of a hand grenade, as suggested by some, but rather the pin that uncouples railway carriages. The expression is thought to derive from North American, possibly Canadian, railroad language, where the pulling of pins from rolling stock would disconnect them thus ending any possibility of further progress.