"NO" is not just a word but it defines courage and audacity. It is always hard to say NO and accept NO. So, either we hate it saying to someone we are close to or fear the consequences of what will happen if someone doesn't accept it. But not saying no frequently can be destructive and this happens with everyone. In extreme situations, we even get caught in an endless loop in which we have an ever increasing outrageous circumstances with no real value of our own selves. We stop thinking about our selves and start living to please others. We even have fear of confrontation and just to avoid building up wrong equation with someone we tend to say YES instead of NO.
Whats wrong in saying NO? and why even do you need to give an explanation for it? we all have right to choose and there are things which you need to do only for you. Remember even if you try you can't please every single person around you. It is your life and your decision if you don't like something say No, if you don't want to go for a party say No, If you don't feel comfortable in someone's company say No. Being honest about your wants and needs will make your more successful and stress free in life. It will always make your relationships more livelier and happy.
So, next time learn to say "NO".