Quote from : The Night Circus Book

Secrets have power,” Widget begins. “And that power diminishes when they are shared, so they are best kept and kept well. Sharing secrets, real secrets, important ones, with even one other person, will change them. Writing them down is worse, because who can tell how many eyes might see them inscribed on paper, no matter how careful you might be with it. So it’s really best to keep your secrets when you have them, for their own good, as well as yours. This is, in part, why there is less magic in the world today. Magic is secret and secrets are magic, after all, and years upon years of teaching and sharing magic and worse. Writing it down in fancy books that get all dusty with age has lessened it, removed its power bit by bit. It was inevitable, perhaps, but not unavoidable. Everyone makes mistakes.