Some time ago I was meditating on relationship and boundary-setting — specifically with a friend who threw a bit of a fit at me. She asked me to do her a big favor, trying to downplay the size of the favor in the asking. I refused (reasonably, I thought); and so she got snippy.
Alison advised me not to answer or argue again: I was in the right, and I should simply let it go. I agreed with Alison — at least, my mind did. But my heart found it hard to accept disappointing my friend.