You can order a quesadilla at Chipotle, even though it’s not on the menu.
Every parent knows this, because it’s the perfect thing to order for little kids — just cheese and a tortilla.
Every parent tells their friends.
Result: Tons of word of mouth.
Why people share: Because it’s a secret. Because it’s special. Because one parent feels smart and helpful when they clue in another parent to the secret.
When it stops: The day they add it to the menu. There’s no reason to tell a friend about something everyone knows about.