Does not doing something on principle, but not telling the other person this, negate the principle?
I'll give an example. I was asked to cover an evening shift at work this morning. But I don't feel like doing a favour because I was cut from two morning shifts and only found out at the last minute. That might sound petty but i feel ive been messed around and it wouldn't get me far if I told my boss that is the reason. So is my principle lost because I am protecting my future interests and not informing them?
As a side note, I believe if you don't want to do a shift you're not scheduled for there doesn't have to be a reason - it's you're own time and feeling guilty about wanting to keep it is just silly. So my question here is more to do with semantics.