Try telling them what may happen one day if they do not fly correctly. We all know that flying is a very dangerous business if you take short cuts, and whilst I do not take pleasure in scaring students with stories, they need to be aware of what can go wrong, and the positive effect on safety of every detail you pick them up on.
Try reading through some recent accident reports with them for inspiration.
Assuming the student has motivation to stay alive, show them how they will decrease their chances of staying so if they don't do as you say!