I have found the best way to get another to acquire a virtue is to impute it to him.” – Winston Churchillcamera lens

Another way to say that is: When you see and appreciate the best in people, and they want to live up to it.

Constructive criticism such as, “I did not appreciate the way you spoke to me in front of our friends, and I want you to be more polite in the future,” rarely leads to improvement.

Instead, try something like this: “Thanks for noticing that I was becoming embarrassed during our interaction in front of our friends. I appreciate that you went along with it when I changed the subject. Now that we are in private, is there more you want to discuss?”