So there's an argument for going into the classroom (as a teacher) completely unprepared, stumble through the material, reason things out in fron of the students, go down hopeless calculations for a while, then say "scratch that", "let's see....hmmmmm", etc....Nothing should be clear, the students would have to make huge efforts just to find out what's on the hw. I know some people like this (not by design). I wonder if their students learn some important life-skills though.