Many times people have a hard time telling others "no". Are you one of those people that fall under guilt as a result of saying no? It feels like a curse, doesn't it?
Saying NO, is powerful and simply okay. Saying NO, to others will let people know that you think for yourself. It lets them know that you value your time, your priorities, needs, and yourself.

Why are do we fear telling other people NO?

Because we fear disappointing them:

Subconsciously, we care about what others think of us. Because we care of the thoughts of others we fear disappointing them, changing the way they perceive us to be. The fear of disappointing others can cause you to be unhappy leaving you to make choices and decisions that you didn't want to make in the first place. You don't want to upset others, causing you to carry that fear of losing that relationship with someone. Sometimes we often take the load of satisfying others on our backs, unknowingly you become a slave to other people. It is impossible to be perfect to anyone and everyone.