Yes, saying No is one of the most hard thing for me to do and I think for many of us it us. Because we actually don't want to hurt the other person/party.
This is its really hard for me to chose yes or No in some situations as the thing I don't want to do but for the sake of the other person I had to enter into the job.
Along with all your valuable information I want to say that we should say No in a way which doesn't bring bitterness in the other person and our relationship with our loved remains intact with love.
A very nice sensible topic it is,thank you for discussing it.