Truth and Deception

I feel that in mathematics, deception may be necessary to knowing. I feel this because I believe that a teacher, when teaching mathematics, may need to use a lie to make the truth clear. The teacher may say "SIN means System In Numbers, right?" to get us all to say "No!" And then think about what it really does mean, not the acronym, but the concept in and of itself. 

Perhaps this can be applied even on an elementary level, such as talking about the commutative and distributive properties. For example, a teacher might say to a student, "So,  5 x 6 = 30, so that means that 5+6 = 30, right? Wrong, it's actually 6 x 5 = 30" and so on. I think that in many cases, deception is necessary to knowing. But I do think that knowing can also be achieved by the truth and the truth is usually a better way to learn.