"Yes," Data says, "but the concept seems deeper than rules or philosophy -- I am curious how it can best be defined for you."

Worf grumbles, he thinks, and ends up throwing his hands up in frustration, saying only, "It is!"

"How does a fish define water?" Picard says to Data, after Worf stomps off to answer a call, and Data tells him that the metaphor helps (much to his own surprise).