Saying "no" is something that comes easy for some and harder for others. I was once a part of "others" but now I am happily part of "some".
Now that I am where I am it has become easier to see why people have a hard time saying "no" and why in other situations they don't. "No" can take all sorts of different forms; "I don't want to go out tonight", "I don't want to go with you", "I don't want to eat that", "I don't want you to do that", or "I don't want to do that". This list is long but ultimately all are saying "no" to whatever it is. I am sure there are many reasons why people have a hard time doing this but essentially it's because they have a fear of disappointing others or letting them down by not wanting to do whatever it is.
If you have a hard time saying "no" you find yourself going places that you don't want to go to, eating things you don't want to eat, dealing with situations that make you feel uncomfortable, and dealing with people that make you feel uncomfortable. Society makes it hard for you to say "no" because saying "no" is rude. Saying "no" is mean, it's anti-social, basically, why would you say "no"? The people around you have a hard time understanding why you wouldn't want to do something or go somewhere, but that isn't for you to explain. You don't need to sit around and tell them why you don't want to do something.
There are many reasons why people should say "no" or we should allow there to be more comfort in saying "no". Saying "no" keeps your peace and your freedom. When someone asks you to do something and you say "no" let go of that guilty feeling. Let go of that feeling that you hurt someone's feelings. If the people you surround yourself are hurt by any of your "no's" then that's their own insecurity battle they have to face. You didn't do anything wrong and if the person you said no to take it personally, that is them, not you. Saying "no" doesn't hurt anyone and could never hurt anyone. You feel guilty for saying "no" because the people around you have conditioned you to think that there is a burden that comes with rejecting an idea or an event, which in fact is a lie.
Not doing something that someone else wants you to do or in any situation where you would have to say "no", doesn't make you a bad person. In fact, you will learn to enjoy the things you want to do more when you learn to turn down things you don't enjoy. You will have more fun and allow your life to look like the way you want it. You won't be spending hours at an event wishing you had said no. You won't be stuck with a friend when you just wanted your alone time. Your life won't look like a constant state of, "I wish I had just said no." And your friends and family not understanding this is not your problem, it's there's.
So, just say "no". Say "no" and let go of the feeling of the worry of hurting someone else's feelings, you aren't going to do that. Enjoy all the things you want to do and leave no room for you wishing later that you had said "no". There is no reason to be stuck doing things or being around people you don't want to. It's okay to cancel things last minute or say "yes" and then "no". That is okay. Your freedom and peace of mind is all that should matter to you.