Patience is also a virtue....a lot of instructors (admittedly knackered old farts in the Air Force) are of the opinion "I can do it - why can't you?". Remember that you were a stude yourself once and that students make more mistakes than most. That's one way people learn. As an instructor, as well as the Demo-Teach-Task cycle, it's your job to analyse the performance sensibly without nagging the stude to death!
Oh what a fine line we tread.....!