Saying YES may be easier, but there's much more power in saying NO.
Here are 3 reasons why saying NO benefits you:
Boundaries - Imagine a game of tug of war, but you're on both sides of the rope. When you always say YES (even to things you don't want to do), your life is pulled around by others. It's like being in the passenger seat of a car and not having any say on where you're going. Draw a line between the things you want (YES) and don't want (NO). Determine what's inside and outside of your boundaries to help communicate and clarify your core values and desires.
Respect vs. Like - Most people don't like to say NO because it lets others down. Instead of being known as a YES-man (or woman), wouldn't you rather be respected because of your honesty to say NO? When you say YES to everyone, you become a hostage in your own skin. You become unhappy with all your obligations, yet have no one to blame except yourself. Saying NO means you understand you can't please everyone. Choose NO and uphold your values.