One theory says that if you treat people well, you’re more likely to encourage them to do what you want, making all the effort pay off. Do this, get that. Another one, which I prefer, is that you might consider treating people with kindness merely because you can. Regardless of what they choose to do in response, this is what you choose to do. Because you can. – Seth Godin
The reason why Seth is right about being kind because you can is that karma* always wins.
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* Being nice because you want something is a quid pro quo and it’s even slimier if the other person doesn’t know it. Don’t do it. Be kind because it’s the right thing to do. Because it makes you feel good – being kind is it’s own reward. And don’t worry, karma will see when you’re kind just because you can be as well.