Trying tell smokers to quit. They know it's bad but still continues. Once health scare, stop. Once health recover, starts again.
Sometimes it is jus hard to change urself. Even harder to change someone else.
On top of what had been mentioned, uncle can share with u a few other things:
1. If u had nothing good to say about the other person, had better not say anything at all.
2. Behavior can be manipulated. But it is impractical and too siong to do this all the time.
3. Lastly, surround urself with like-minded people or people u aspire to become. Group think/herd mentality. You cannot become better by hanging out with people who are filled with negative thoughts or constrained by their own experiences.