If you want to convince someone of something you don't think they'll believe, tell them a secret. Secret information always seems more valid and trustworthy than public information. Use language like: “I'm telling you this in strictest confidence” or “I shouldn't be telling you this, but” or “If you promise to keep it a secret."
And if you want to get the other side to commit to something, use the magical three-step formula that has been used throughout history, and especially by our spies in World War II:
- Tell a secret
- Make a confession
- Ask a favor