More from How To Win Friends And Influence People:
Jesse James probably regarded himself as an idealist at heart. … The fact is that all people you meet have a high regard for themselves and like to be fine and unselfish in their own estimation. J. [P.] Morgan observed … that a person usually has two reasons for doing a thing: one that sounds good and a real one. The person himself will think of the real reason. You don’t need to emphasize that. But all of us, being idealists at heart, like to think of motives that sound good. So, in order to change people, appeal to the nobler motives. …
When the late Lord Northcliffe found a newspaper using a picture of him which he didn’t want published, he wrote the editor a letter. But did he say, “Please do not publish that picture of me any more; I don’t like it”? No, he appealed to a nobler motive. He appealed to the respect and love that all of us have for motherhood. He wrote, “Please do not publish that picture of me any more. My mother doesn’t like it.”
I doubt that people have more trouble thinking of ideal vs. non-ideal reasons for doing things. So why do you persuade better by pointing to ideal reasons for something you’d like people to do? Because you implicitly offer a complement to an idealistic act: recognition. People are more eager for others to recognize idealistic acts, vs. other acts. If they follow your suggestion to do something for which you’ve offered an idealistic reason, they know you are available to tell others of their idealism. Which makes that idealism worth much more.