The sweet YES could give you enduring problems when a simple, polite NO is just like a bitter pill
Yes is a very humble word. People will always expect yes from the other. We usually say 'yes' just to be nice although we do not really mean 'yes'. However, this is where problems surfaces. Saying no is not a selfish attitude. It's their need and want, not yours saying no means you do not want to promise on things you are not going to do as in helping other people