I'm talking about you, the recruiter, realizing that either A) this is not the right candidate or B) this is not the right job after the interview is scheduled.
Sure, in a perfect world we already have decided that there's a fit - but what if additional information comes to light on either side that says you were wrong? What if you KNOW deep down that the right thing to do is cancel? How do you deliver that to the hiring manager AND the candidate tactfully?
I am stealing that line. :)