It took me a long time, but I discovered, if you say, "No", it's not the end of the world and most people are fine with it and say, "Okay." If they're not, are they really your friend? It's also not necessary to explain yourself. I got to the point where I was tired of being angry at myself for saying, "Yes", to things I did not want to do and not enjoying the situation I was in. I was told, the older you get, the less you care about what others think. I don't know if that's true or not. I think everyone gets to the point of standing up for themselves in their own time.