"I am the Guardian of the Gates and since you demand to see the Great Oz I must take you to his palace. But first you must put on the spectacles."
"Why?" asked Dorothy.
"Because if you did not wear spectacles the brightness and the glory of the Emerald City would blind you. Even those who live in the City must wear spectacles night and day. They are all locked on, for Oz so ordered it when the City was first built, and I have the only key that will unlock them."
L. Frank Baum
in The Wonderful Wizard of Oz