Don't Put All Your Eggs in One Basket

Usually credited to Miguel de Cervantes, whose novel Don Quixote (1605-1615) advises that a wise man shouldn't "venture all his eggs in one basket." Cervantes almost certainly didn't invent the saying himself, though; very similar proverbs appear in Italian proverb collections of the same period, including Giovanni Torriano's A Common Place of Italian Proverbs (1666), suggesting a shared Spanish or Italian folk origin that Cervantes simply popularised in print. The underlying logic is straightforwardly practical: a dropped basket of eggs, all in one place, breaks the lot at once.