Most people prefer to see themselves as fair, generous, and competent. Even when they act selfishly, they keep a story in which they are still “the good person.”
If you want to persuade, speak to that better self. Frame your request as an opportunity to act in line with their values: responsibility, loyalty, professionalism, kindness.
This isn’t flattery. It’s choosing a doorway that doesn’t insult. When you assume the worst motive, you invite the worst behavior. When you appeal to a higher motive, you give them a respectable way to agree.
Make the appeal concrete and believable. Tie it to something they’ve already done well. Let them feel consistent with their identity.
Agreement lands easier when it feels like dignity, not defeat. Offer that, and resistance weakens.