I've realized when you know something you're trying to keep secret, there is usually one person whom you most want to not know -- that if they found out, would be more disastrous for you than any other person finding out. What would we call that one person?
(If you're trying to not tell, it's important to know who that one person is, so you can concentrate your efforts on not telling them. I once let something slip in front of such a person, being caught off-guard; and was much embarrassed as a result.)
Please don't edit or XY this question. An answer that doesn't specifically address the question as asked is no answer.