One of the best ways to keep a great secret is to shout it.
Notes from Wikiquote
Land was not the first to make such observations; in One Man in His Time (1922), p. 162, Ellen Glasgow has a character state | Half the time when he is telling the truth, it sounds like a joke, and that keeps people from believing him. He says the best way to keep a secret is to shout it from the housetops; and I've heard him say things straight out that sounded so far fetched nobody would think he was in earnest. I was the only person who knew that he was speaking the truth.