The story
Allusion to “The Goose that Laid the Golden Eggs”, one of Aesop’s Fables. Attested from the 18th century. Compare golden goose, kill the goose that lays the golden eggs.
Etymology from Wiktionary, CC BY-SA 4.0.
golden egg
Today it means: A source of consistent profit or advantage, or the profit gained by such advantage. Full definition →