Too much pride in not listening to what I'm telling them to make it better. Whether it's jerking the trigger, limp wristing, anticipation of recoil and forcing the gun down..etc.
That's a tough nut to crack in any kind of instruction. Unfortunately, students with that kind of approach seem to want to think that if they simply practice it (incorrectly) a bazillion times, it will somehow magically resolve itself into being correct. Male students are worse than fem students, in any subject, shooting related or otherwise.
Sgt Lumpy - n0eq