Isn't the point of you going out with an instructor, for you to take the controls at some point? Or is this an existential musing on the risks for instructors?
Having done many trial lessons of the 'red letter day' kind in my last job, you stay alert as it's possible to be, while giving the punter the opportunity to experience the controls. But the risk is there, has always been there, and always will. Heard a few scary stories though, m