Yeah, I do a lot of that. Also, when my son is getting off track, I (deliberately) lead him into a contradiction, which causes him to think about where he went wrong. I used to annoy my teachers because that was also my most favorite form of proof, by contradiction. It is also something I employ a lot here on math teach. It seems to be contra the thinking of most people. They seem (overly) used to A, then B, then C.