the.com/goldmine

Proof that the real money is always in whatever nobody bothered to dig yet.

means A source — a business, idea, or asset — that keeps producing wealth or valuable results, often more than expected.

from Literal at first: an actual mine yielding gold. English speakers started using it figuratively from the 1800s onward for anything that generates riches with similar reliability — the leap from 'hole in the ground that pays off' to 'any venture that pays off' was an easy, obvious one, and it stuck.

origin
literally meant a gold-producing mine, 1829
figurative shift
metaphor for profitable asset emerged by 1882
linguistic irony
most goldmines never actually struck gold
modern usage
now describes data, not dirt
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