The two rules of instructing (gliding, but probably also applies to power)
Rule 1 Bloggs (the student) is out to get you.
Rule 2 The more Bloggs learns, the more devious he becomes in applying Rule 1
However the instructor is not supposed to show that he is aware of these rules at any time, even when the roundout has just gone horribly wrong!
Spare a thought for P1.