"There was no such thing as luck.  Luck was a word idiots used to explain the consequences of their own rashness, and selfishness, and stupidity.  More often than not bad luck meant bad plans."

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A margin of safety is achieved when securities are purchased at prices sufficiently below underlying value to allow for human error, bad luck, or extreme volatility in a complex, unpredictable and rapidly changing world.

— Seth Klarman