When you smile at someone and they smile back, you automatically feel better. Even if they don't smile back, you will feel better because you know the most destitute（穷困的） person in the world is the one without a smile. You immediately become richer by giving that person yours. 

The same goes for the compliment. When you sincerely compliment a person or extend him a courtesy, he is going to receive a direct benefit and like himself better. It is impossible for you to make someone feel better and no feel better yourself.