Sometimes saying, 'no, thank you,' is the hardest thing you'll do. It's hard because we think we need to use more words than we do. It's a habit we've picked up, I think, (or a coping mechanism) because lying is so pervasive in our culture. Surface is pervasive, using is so pervasive that when we are sincere, it sounds, especially to an ear not attuned to the pitch of our sincerity, false.
So, the hardest thing to do, aside from saying 'no, thank you,' is leaving it at 'no, thank you.' We want to explain ourselves, to rip ourselves open, head to heart and say, 'Look! Look! I'm not hiding anything. I really am this lost/this uncomfortable/this wrong for this situation.' But we can't. We can't. Because we are not responsible for how we are perceived.
Okay. Maybe I was wrong. Maybe *that's* the hardest thing. Not the saying no, but the not being believed, the lack of the assumption of sincerity and genuineness from the other party. That's what hurts. Because we're all of us doing our best with what resources we have in the moment we're in. We can do no better, and we can't live otherwise.