Sometimes it is so hard to say No to someone's request while other times it's easy. There are many things that come into play when someone asks you to do something.
If I already have another commitment at the same time, no problem. Sorry, I say, we are busy. But if I am not busy and they know that (usually because the first question was "Are you free Saturday night?") I have a harder time of it. I think the guilt of being impolite or hurting their feelings comes into play.
Our friends invited us to a concert and we were busy. I didn’t really look into the artist because well, we were busy. It turns out she had the wrong date and now we weren't busy. Once we looked into the artist, we weren't interested.
Sure we liked the artist, but not enough to pay for it nor take our time to go. I felt guilty saying no. I explained why, but still it felt like an insult.
The Japanese would never say no to an invitation. It is considered rude in their culture to do so. Now that we are trying to simplify our lives, we really evaluate what we do, especially social events that are time sensitive.
My rule lately is to say Yes when I can and when it feels right. How do you feel when you say No because it doesn't fit well into your life?