I'm surprised by the number of answers, yet no-one managed to give a completely correct descriptopn of when you get WLTKD (although Gothmog was closest).
To have WLTKD in a city, the following must be true:
* The city must have size of at least 6
* The city cannot be shrinking (i.e., it must produce at least twice as much food as its size)
* There cannot be any unhappy citizens or resistors.
* The number of happy citizens must be equal to or greater than the number of content/specialist citizens (i.e. at least half of the citizens).
So a sixe 6 city will be in WLTKD with 3 happy and 3 content/specialist citizens as long as it produces at least 12 food.