a magician never reveals his secrets

Said by someone who does not wish to divulge or explain something (not necessarily an actual magician). A: "What did you put in this sauce? It tastes even better than usual!" B: "Ah, a magician never reveals his secrets." Mommy, I tried to ask the magician how he did that trick, and all he would say is, "A magician never reveals his secrets." A: "That toy has been sold out everywhere! How did you get one?" B: "Oh, a magician never reveals his secrets."