L. Frank Baum, The Wizard of Oz

Dorothy: “Oh, will you help me? Can you help me?”
Glinda: “You don’t need to be helped any longer, you’ve always had
the power to go back to Kansas!”
Dorothy: “I have?”
Scarecrow: “Then why didn’t you tell her before?”
Glinda: “Because she wouldn’t have believed me.
She had to learn it for herself.”